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Thin-film structures with nanocrystals an origin of enhanced
photo-response
O Goncharova1 2 3
R M Montereali2 and G Baldacchini
2
1 Institute of Physics National Academy of Sciences 68 Independence Avenue
Minsk 220072 Belarus 2 Frascati Research Center Ente per le Nuove Technologie lEnergia e lAmbiente 45
E Fermi Street Frascati 00044 Rome Italy
E-mail OlgaGoncharova08gmailcom
Abstract To discover well the properties of nanothin crystalline layers and nanometer-sized
crystals we investigated the relatively thick multilayer structures composed of high quantity of
nanothin layers with nanocrystals Alternate nanolayers of 150ndash10 nm thicknesses with LiF
CaF2 and CdS nanocrystals have been deposited onto irradiation-resistive substrates by thermal
evaporation of pure crystals Some multilayers were γ-irradiated in air at room temperature
with dose of 83 kGy X-ray diffraction and microscopy studies reveal that the multilayers
consist of nanocrystals with cubic phase and defined size Thin-film structures were oriented
along the (111) plane Absorption spectra of non-irradiated LiF nanocrystals of 100 nm size
suggest evidence of metal colloids presence We find that photoluminescence spectra of γ-
irradiated nanostructures with metal colloids and various LiF contents show the enhancement
of F3+-colour centres excitation in the region of metal colloids absorption and the increase is
observed of the emission intensities ratio of F3+ and F2 centers with respect to initial crystals γ-
coloured in identical conditions Emission intensities of both centers under excitation at 458
nm correlate with LiF content These effects which are related to high-quality nanostructures
but at the same time depend strongly on the defect content especially as far as their 1ndash2 ps
nonlinearities are concerned could depend on nanocrystal purity and metal excess collection in
their boundaries regions Our results provide an original contribution to the understanding of
the influence of the nanolayer-by-nanolayer deposition γ-irradiation on these specific
structures and of the metal aggregates on the properties of nanocrystals and nanolayers
1 Introduction
Nano-sized layers films crystals and multilayers play an important role in future technology as they
exhibit different and often unique properties with respect to the initial macroscopic materials [1ndash6]
Film structures with nanocrystals have attracted much interest for the possibility to grow them in their
final position within switching devices detectors efficient dosimeters emitters and solar cells The
possibility of using these nanostructures not only for fundamental studies but also for novel devices
fabrication is stimulating the efforts to control the nanocrystal size shape structure space arranging
as well as their composition and structural defects Unfortunately not only bulk but boundary
(surface) states of nanolayers and nanocrystals affect strongly their properties as their size reduces [1
7] The properties of the nanoelements as prepared and post-growth processed by different methods
3 To whom any correspondence should be addressed
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
ccopy 2010 IOP Publishing Ltd 1
can be affected by the presence of various defects and also by aggregation of impurities and intrinsic
defects to the colloids in the bulk and surface regions related to the used preparation technique
Several physical deposition methods are usable for preparation of thin films and nanostructures such
as laser-assisted electron-beam or thermal evaporation from composite targets and undoped bulks
sequential sputtering or evaporation [1ndash6 8] Ion implantation [9] thermal treatments [10] and
ionising radiation bombardment (combined with special annealing [11ndash14]) are established tools for
metal nanoparticles formation in solids Understanding the structural evolution during the preparation
of nanocomposites can be of great help in understanding how to control the characteristics of the final
products readily
Lithium fluoride is a well-known material which after irradiation by ionizing radiation (electrons
ions γ-rays and X-rays) or laser light is characterized by F-colour centres (CCs) aggregates [3ndash5] and
metal colloids formation sensitive to the content of oxygen hydroxyl and divalent metal ions in initial
crystals [11ndash14] Clusters of F-CCs (lithium colloids) and impurity colloids can be created in the
irradiated regions of LiF and at temperatures where diffusion of the defects is possible [10ndash12] Even
though the actual mechanism of the formation of such colloids is still an open question a lot of
attention was devoted to study optical properties of the crystals and their near surface nanothin layers
containing these metallic aggregates Since thin-film nanolayers and nanocrystals have been studied
only in a limited way in this paper we carried out the following measurements to investigate them
2 Experimental details and measurements
Microstructural and optical characteristics of the investigated samples are summarized in figures 1ndash8
The experimental samples are multilayers and thin-film interferometers (TFIs) with the intermediate
multilayers [15ndash17] Each structure unit is a thin-film nanolayer with a nanocrystal array inside it
(figures 1 2) The geometry of the nanostructures can be tuned by controlling the thicknesses and the
compositions of the ldquosensitizingrdquo and complementary buffer nanolayers Every nanolayer can be
designed of one material [15] and as composition of nanocrystals clusters of two materials [16]
Figure 1 Schematic representation of the periodic multilayer nanostructures with c-oriented
nanocrystals prepared from one (a) two (b) and more than two initial materials (c)
21 Samples preparation
The elaborated samples consist of dielectric (LiF CaF2) orand semiconductor (CdS) nanocrystals
Samples with various ldquosensitizingrdquo nanocrystals are grown on radiation-resistant flat substrates in the
layer-by-layer manner of the reproducing of thin-film nanolayers with defining compositions [15 16]
ldquoSensitizingrdquo nanolayers are prepared with thicknesses equal to nanocrystal sizes [15] and by using
special techniques for nanocrystal ordering [17] The approach presented in this paper can be extended
to fabricate thin-film multilayer structures of a wide range of materials To avoid radiative coloration
thermal evaporation was the preferred fabrication technique Undoped crystals 99999 pure are
used as starting materials The clean substrates were kept at room temperature (RT) on a copper
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
2
holder and the vacuum pressure in the evaporation chamber was about 10ndash6
Torr The films
thicknesses were measured by interference method As-prepared (fresh) samples are kept for seven
days in a dry box before starting the optical measurements in the open atmosphere at RT at about 50
humidity Crystals and films produced in the manner of continuous growth of the result thicknesses
were used as reference samples After the growth some samples were γ-irradiated at RT up to 83 kGy
[19] Self-assembled nanolayers of LiF and CaF2 nanocrystals were used as templates In the case of
CdSeCaF2 CdSCaF2 [20] and LiFCaF2 nanostructures (figure 2) more radiation-resistant crystalline
CaF2 nanolayers were used to promote the c-axis ordering and the size restriction of ldquosensitizingrdquo
CdSe CdS and LiF nanocrystals After thermal evaporation and post-growth γ-colouration spatially
ordered arrays of CCs could be fabricated in the periodic multilayer nanostructures (figure 1b) [6]
(c)
Figure 2 XRD and SEM images of non-irradiated thin-film structures with c-oriented nanocrystals of
cubic phase and defined sizes prepared from LiF (a) CaF2 (b) and LiF and CaF2 initial crystals (c)
22 Samples characterization
The microstructure of thin-film samples is determined by X-ray phase analysis scanning electron
microscopy (SEM) and atomic force microscopy (AFM) The c-axis ordering (texture) analysis of
thin-film nanostructures was performed by means of pole figures and θ-2θ diffraction patterns (figures
2ndash6) A Seifert XRD 3003 PTS four circles diffractometer employing CuKα (λ= 154059 Aring) radiation
was used for pole figure measurements The primary beam was collimated by a 05 mm pinhole and a
1 mm slit was placed in front of the detector The accelerating voltage and current was fixed at 40 kV
and 30 mA respectively Pole figures were recorded varying between 0deg and 360deg with a sampling
interval of 4deg and varying χ between 0deg and 75deg with Δχ=25ordm The acquisition time was 5 seconds X-
ray θ-2θ diffraction pattern were collected by using a Rigaku Geigerflex diffractometer with CuKα
radiation The diffractometer was equipped with a graphite monochromator in order to suppress Kβ
radiation and to increase signal to noise ratio The divergence slit scattering slit and receiving slit
were 05ordm 045deg and 03ordm respectively The measurements were performed with a sampling interval of
005deg and a fixed time of 10 seconds
Optical transmittance (T) and reflectance (R) spectra of samples are measured with a dual beam Cary
500 Scan and a Lambda 19DM Perkin-Elmer spectrophotometers in the spectral range 190ndash3300 nm
(figures 6 8) Optical absorption (OA) (figure 7) is derived from transmittance and is used to estimate
the defects in nanocrystals with respect to initial crystals The photoluminescence (PL) measurements
were carried out by using a Jobin Yvon Fluorolog-3 spectrofluorometer with the front-face detecting
geometry by exciting the samples at the wavelength of 458 nm (M-band LiF) see figures 7bc
Nonlinear properties were detected using a pump-and-probe technique and 3-ps [11ndash15] and 150-fs
laser pulses [3 5] and reported in figure 8 All measurements were performed at RT
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
3
3 Thin-film structures with dielectric nanocrystals
31 Thin-film structures with nanocrystals of one fluoride material
X-ray diffraction (XRD)- SEM- and AFM-results show that non-irradiated multilayers are structures
with definite size of nanocrystals (Final thickness of LiF CaF2 and LiFCaF2 structures is
approximately 65 μm) Presence of (111) and (222) peaks in XRD data of the multilayers indicates
that they have c-axis orientation perpendicular to the substrate surfaces The XRD patterns of LiF and
CaF2 multilayers see figure 2 show intense (111) peaks at 2θ = 387ordm 283ordm and a considerably less
intense (222) peaks at 2θ = 831ordm 585ordm respectively Not-presented here XRD- SEM- and AFM-
results validate the fact that irradiation neither causes a change in the packing nor increases the size of
nanocrystals The (111) peaks prevail in the XRD-patterns of samples and γ-irradiation with the dose
of 83 kGy only improves the crystallinity and the orientation of nanostructures (increase in the
intensities of (111) peaks) The XRD results correlate well with the texture analysis (figures 3ndash5)
(a)
(b) (c)
Figure 3 2d and 3d (111) (200) and (220) LiF pole figures of the non-irradiated LiF
nanostructures (a) Magnification of (111) LiF pole figure in the region χ lt30deg (b)
and -scan of the (200) LiF pole figure demonstrating the in-plane isotropy (c)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
4
In figure 3a two (2d) and three dimensional (3d) (111) (200) and (220) LiF pole figures of the non-
irradiated LiF sample are reported A sharp (111) texture is present The Full Width at Half Maximum
(FWHM) of the pole located at χ=0 in the (111) pole figure is about 6deg and the FWHMs of both (200)
and (220) poles are 8deg This is due to a very low mosaic spread in the growth direction Figure 3b
shows a magnification of the (111) pole figure in the range χ lt30deg The isointensity lines were chosen
in the following way the intensity of the nth line is In = Imax2n The circular shape of the pole indicates
that the in-plane nanocrystal distribution is uniform This hypothesis is supported by the analysis of
the cut of the (200) pole image at χ=55 shown in figure 3c no difference in intensity is observable
varying angle confirming that any preferential in-plane direction does not exist
The (111) (200) and (220) LiF pole figures for the γ-irradiated LiF sample are shown in figure 4 For
this sample perfect (111) texture is presented (a) The FWHM of the (111) (200) and (220) LiF poles
are 5deg 8deg and 7deg respectively The detailed (111) pole in the range χlt30deg (b) and the cut of the (200)
pole figure at χ~55deg (c) are also reported The (111) LiF pole profile is perfectly circular and the (200)
pole -scan is constant indicating a high in-plane isotropy differently from what we observed for non-
irradiated LiF sample in which a low fraction of slightly misoriented nanocrystals can be inferred
(a)
(b) (c)
Figure 4 2d and 3d (111) (200) and (220) LiF pole figures of the γ-irradiated LiF
nanostructures (a) The perfect texture is shown Magnification of (111) LiF pole
figure χ lt30deg (b) and -scan of (200) figure demonstrating in-plane isotropy (c)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
5
It must be emphasized that the difference is very small an analysis of the (111) LiF pole figures
revealed that the integrated intensity of the range χlt10deg (Iχlt10) to the integrated intensity of the total
(111) pole figure (Itotal) ratio varies from 1495 (for the non-irradiated LiF sample) to 1505 (for the
sample γ-irradiated at RT with dose 83 kGy) Conversely the pole maximum is incresed of about 20
in the irradiated sample confirming the effect of the structure improving due to the γ-irradiation
In figure 5 the (111) (400) and (220) CaF2 pole images of non-irradiated CaF2 sample are reported (a)
Also in this case the presence of a good (111) texture is evident The FWHM of (111) (400) and
(220) poles are 5deg 7deg and 7deg The (111) peak profile is circular down to the lowest intensity and no
evidence of peak broadening was observed The pole is misaligned respect to the centre of about 05deg
as can be seen in figure 5b Since the measurement was repeated several times an error in the
mounting of the sample can be excluded A different profile of the -scan performed on the (400) and
(220) poles was recorded (figure 5c) characterised by a weak intensity dependence vs This
behaviour is due to the (111) CaF2 direction not exactly perpendicular to the substrate surface
(a)
(b) (c)
Figure 5 2d and 3d (111) (200) and (220) CaF2 pole figures of non-irradiated
CaF2 nanostructures (a) Magnification of (111) CaF2 pole figure χ lt30deg (b) A
misalignment of ~05deg is present and is consistent with the (400) (220) -scan (c)
Not reported here the poles for the γ-irradiated CaF2 sample revealed the development of more strong
(111) texture The FWHM of the (111) pole is about 4deg indicating a very small mosaic spread
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
6
32 Thin-film structures with nanocrystals of various fluoride materials
To establish the influence of content of LiF nanocrystals with given size on PL spectra of multilayers
two LiFCaF2 structures have been prepared The first LiFCaF2(1) (figure 1b period 1) is the 48-
period structure of 100 nm LiF-nanolayers and 50 nm CaF2-nanolayers The next LiFCaF2(2) is the
24-period structure consisting of 100 nm LiF- and 220 nm CaF2-nanolayers (figure 1b period 2)
(a) LiF (111) LiF (111) CaF2 (111)
Figure 6 3d (111) LiF CaF2 pole images of fresh LiFCaF2(1) (left) and LiFCaF2(2) multilayers
(middle right) (a) XRD patterns of LiFCaF2(2) before (1) after irradiation (2) and fresh LiFCaF2(1)
(3) (b) Transmission spectra of the multilayers and substrate (c) Reflection spectra of LiFCaF2(1) vs
angles of incidence in the range 20ordmndash50ordm (d) The graphs are p-polarized light
Both multilayers were composed of ~100 nm LiF and ~50 nm CaF2 nanocrystals and were c-oriented
structures (figures 6ab) In figure 6a the (111) LiF and CaF2 pole images of as-prepared LiFCaF2(1)
(left) and LiFCaF2(2) samples (middle right) are reported A well-resolved (111) LiF texture is
present on both cases The quantity of used isolines are 128 and the minimal and maximal intensities
in the (111) LiF pole figures are about 910 and 283 cps for the LiFCaF2(1) samples and 450 and
1154 cps for the LiFCaF2(2) samples This is due to the result LiF thickness in the LiFCaF2(1)
sample (45 μm) 27 time larger with respect to the LiFCaF2(2) sample (17 μm) The CaF2 pole image
(figure 6a right) indicates that the preferential nanocrystal orientation is (111) direction The
crystallinity and (111) texture improving for the γ-irradiated LiFCaF2 samples is supported by the
XRD patterns shown in figure 6b strong difference is observable between the data measured for
LiFCaF2(2) before (curve 1) and after γ-irradiation at RT with dose 83 kGy (curve 2)
High-reflectivity and transmissivity bands are provided by the LiFCaF2 structures (figure 2c) Spectral
positions of the bands were not changed after γ-irradiation but were sensitive to the polarization state
and angle of incidence of light see figure 2d The LiFCaF2 structures covered at the surface by CaF2
nanolayers are more mechanically stable and resistant to external influences than LiF nanostructures
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
7
33 Optical absorption features of non-irradiated thin-film structures
OA spectra of non-irradiated LiF nanostructures and initial crystals with small content of Mg2+
O2ndash
and OHndash ions [13] show well-resolved absorption of Mg
2+ colloids [11 12] (figure 7a) (The non-
irradiated and γ-irradiated substrates remain non-absorbing in the above spectral range) According to
the literature besides Mg colloids with the absorption band peaked at 44ndash46 eV the low-wavelength
absorption band at 36ndash41 eV related to the formation of more large Mg colloids or intrinsic Li
colloids [11 12] are reliably distinguished in non-irradiated LiF nanostructures (figure 7a) [21] and
initial crystals γ-irradiated with various doses and bleached by annealing after irradiation (figure 7a
insert) [13 14]
Figure 7 OA spectra of non-coloured (a) and PL spectra of γ-coloured nano (bold curve) and bulk
(solid curve) crystalline structures (b) and the structures with various LiF contents (c)
34 PL spectra of the irradiated thin-film structures
Non-presented here PL spectra of γ-irradiated CaF2 nanocrystals are composed of the reference 425
nm band excited at the wavelength of 370 nm The PL spectra of initial LiF crystal LiF and LiFCaF2
nanostructures having the same size of LiF nanocrystals and irradiated in analogous conditions are
given in figures 7bc In comparison with the initial crystals an increase of F3+-CCs excitation in the
region of Mg colloids absorption in nanostructures is observed together with an enhanced emission in
the green region with respect to the red one for γ-irradiated film structures (figures 7b) The
normalized emission spectra of nanostructures with various LiF content (bold) have the same shape
the F3+ photoluminescence band intensity at λmax = 538 nm increases of the same factor in comparison
with the F2 emission at 670 nm with respect to the spectrum of the crystal (solid curve) The PL
spectra show an increase (correlated with LiF nanocrystal content) of the intensities of F3+ and F2
bands (figure 7c) These results could be explained by the high structural and optical qualities of these
nanostructures (the overall emission is proportional to the quantity of luminescent LiF nanocrystals)
and by the nanocrystal purity with metal excess collection in their boundaries regions [22]
4 Thin-film structures with semiconductor and dielectric nanocrystals We measured nonlinear optical (NLO) effects for the reference films (figure 8a curve 1) elaborated
multilayers (figure 8a curves 2 3) and specially-elaborated multipeak TFIs containing c-oriented
cubic CdS nanocrystals of defined sizes as reported in figure 8 Sample 3 and TFIs intermediate layers
are composite film structures with semiconductor (CdS) and dielectric (CaF2) nanocrystals (figure 1c)
Separation of the transient shift and absorption saturation in TFIs gives us the features of both effects
Characteristic 1ndash2 ps decay of the shift confirms the metal clusters nature of the effect [23 24]
Maximal NLO effects in nanocrystals are increased with size reduction and are enhanced by extra
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
8
excitation power pulse durability [20 22] and γ-irradiation [19] These effects can be explained by
accumulation of colloids and electrons at nanocrystal boundaries
Figure 8 NLO characteristics detected for (a) reference films (1) multilayers (2 3) (b) multipeak
TFIs with c-oriented cubic CdS nanocrystals of defined sizes (c) Transmission spectra of the TFI
before (B) and at time of excitation (time delay between the excitation and registration is zero) (A)
Impurities and nonstoichiometric excess tend to be expelled from the small crystalline core as the
distance a defect or impurity must move to reach the surface of a nanocrystal is very small
Self-purification of the nanocrystals can be explained through technological arguments and is an
intrinsic property of defects in nanocrystals prepared by the methods of alternative deposition of
nanolayers with thicknesses 150ndash10 nm Post-growth thermal treatments ionising radiation
bombardment and light irradiation of the nanocrystals are the next tools for the nanocrystal
purification metal colloids formation and the nanocrystal properties modification
5 Conclusion
The c-axis highly oriented thin-film multilayer structures composed of dielectric (LiF CaF2) and
semiconductor (CdS) nanocrystals prepared by thermal evaporation show enhanced photo-response
which is related to high-quality nanocrystals but at the same time depends strongly on the defect
content especially as far as their 1ndash2 ps nonlinearities are concerned Critical factors are nanocrystal
purity as well as metal impurities and nonstoichiometric excess collection in their boundaries regions
The nanostructures (more high-quality than original bulk structures) can be part of efficient emitting
elements detectors and modulators of light as well as a novel type of dosimeters Such optically
stimulated luminescence dosimeters (integrable with SiO2OH fibres) provide capability for remote
monitoring radiation locations which are difficult to access and hazardous These devices are relatively
simple small in size cheap in production and have low power consumption Moreover they are also
suitable for space radiation dose exploration In addition they can be used in other radiation
measurements and have interesting perspectives in the case of periodical nanostructures composed of
the nanolayers of CdS and LiF nanocrystals with high-contrast indices of refraction (figure 1c)
Acknowledgments
The authors are indebted to O Bilan A Pace and V Gremenok for their help in irradiation and
microstructure testing of the samples Many thanks are due to M A Vincenti S Tikhomirov and O
Buganov for their assistance during PL and NLO experiments This work is supported by the
Belarusian National Program for Crystalline and Molecular Structures Research Project CMS-35 and
by the grants of the ENEA Fellowships Programme (Frascati Research Center Rome Italy)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
9
6 References
[1] Poole Ch and Owens F 2003 Introduction to Nanotechnology (New York John Wiley)
[2] Goncharova O 1994 Semiconductor microcrystallites in thin-film matrix fabrication methods
optical properties and application prospects New Materials for Thin Film Functional
Electronic-Technological Components ed V Labunov (Minsk Nauka i Tekhnika) chapter 6
pp 99ndash176
[3] Baldacchini G Cremona M dAuria G Martelli S Montereali R M Montecchi M Burattini E
Grilli A and Raco A 1996 Nucl Instr Meth B 116 447ndash51
[4] Montereali R M 2002 Point Defects in Thin Insulating films of Lithium Fluoride for Optical
Microsystems Ferroelectric and Dielectric Thin Films (Handbook of Thin Films Materials
vol 3) ed H S Nalwa (New York Academic Press) chapter 7 pp 399ndash431
[5] Kumar M et al 2005 J Phys D Appl Phys 38 637ndash41
[6] Goncharova O 2005 Microstructure and properties of periodic multilayer thin-film structures
with nanocrystals Advances in Spectroscopy for Lasers and Sensing Proc NATO Advanced
Study Institute (Erice Sicily Italy 6ndash21 June 2005) (NATO Science Series II
Mathematics Physics and Chemistry vol 231) ed B Di Bartolo and O Forte (Berlin
Springer) p 556
[7] Goncharova O Karpushko F V and Sinitsyn G V 1983 Technical Physics 28 1142ndash44
[8] Pulker H K 1979 Appl Optics 18 1969ndash77
[9] Wang Y H Lu J D Wang R W Mao Y L and Cheng Y G 2008 Vacuum 82 1220ndash23
[10] Bryukvina L I Ermolaeva E A Pidgurskii S N Suvorova L F and Khulugurov V M 2006 Phys
Sol State 48 68ndash72
[11] Schwartz K K Lyushina A F and Vitol A Ya 1969 Sov Phys Sol State 11 1885ndash90
[12] Lushchik A Lushchik Ch Schwartz K Vasilchenko E Papaleo R Sorokin M Volkov A E
Neumann R and Trautmann C 2007 Phys Rev B 76 054114
[13] Baldacchini G Goncharova O Kalinov V S Montereali R M Nichelatti E Vincenti A and
Voitovich A P 2007 Phys Status Solidi C 4 744ndash48
[14] Baldacchini G Goncharova O Kalinov V S Montereali R M Vincenti A and Voitovich A P
2007 Phys Status Solidi C 4 1134ndash38
[15] Goncharova O and Demin V 1993 Photosensitive resistive nonlinear optical thin-film
heterostructures RF Patent 2089656
[16] Goncharova O and Demin V 1994 Photosensitive resistive nonlinear optical composite films
RF Patent 2103846
[17] Goncharova O and Demin V 1994 Narrow-band thin-film FabryndashPerot interferometer RF
Patent 2078358
[18] Goncharova O 1998 Light-induced ultrafast bleaching in films of different arranging of
semiconductor nanocrystals materials Proc Int Conf on Coherent and Nonlinear Optics
(Moscow Russia 29 June ndash 3 July 1998) (Moscow Moscow State University Press) p 246
[19] Goncharova O Kalinov V and Voitovich A 2004 Radiat Meas 38 775ndash79
[20] Goncharova O 1996 Picosecond all-optical switching in thin-film FabryndashPerot interferometers
and cavityless devices Notes and Perspectives of Nonlinear Optics (Nonlinear Optics vol 3)
ed O Keller (London World Scientific) pp 636ndash42
[21] Goncharova O and Gremenok V 2007 Comparative study of electronic structure of thin film
nanocrystals prepared by low-temperature vacuum deposition Proc Int Conf CLEOEurope-
2007 (Munich Germany 17ndash22 June 2007) p 1-1
[22] Goncharova O Montereali R M and Baldacchini G 2008 Abstr Int Conf ICL-2008 Lyon
France 7ndash11 July 2008) p 160
[23] Goncharova O 1996 Studies on a Nature of the Picosecond Transient Absorption in Thin Films
Activated by Semiconductor or Metal Nanocrystals Proc Int Conf EQEC-1996 (Hamburg
Germany 8ndash13 Sept 1996) p 87
[24] Z Lu and K Zhu 2008 J Phys B At Mol Opt Phys 41 185503ndash09
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
10
Thin-film structures with nanocrystals an origin of enhanced
photo-response
O Goncharova1 2 3
R M Montereali2 and G Baldacchini
2
1 Institute of Physics National Academy of Sciences 68 Independence Avenue
Minsk 220072 Belarus 2 Frascati Research Center Ente per le Nuove Technologie lEnergia e lAmbiente 45
E Fermi Street Frascati 00044 Rome Italy
E-mail OlgaGoncharova08gmailcom
Abstract To discover well the properties of nanothin crystalline layers and nanometer-sized
crystals we investigated the relatively thick multilayer structures composed of high quantity of
nanothin layers with nanocrystals Alternate nanolayers of 150ndash10 nm thicknesses with LiF
CaF2 and CdS nanocrystals have been deposited onto irradiation-resistive substrates by thermal
evaporation of pure crystals Some multilayers were γ-irradiated in air at room temperature
with dose of 83 kGy X-ray diffraction and microscopy studies reveal that the multilayers
consist of nanocrystals with cubic phase and defined size Thin-film structures were oriented
along the (111) plane Absorption spectra of non-irradiated LiF nanocrystals of 100 nm size
suggest evidence of metal colloids presence We find that photoluminescence spectra of γ-
irradiated nanostructures with metal colloids and various LiF contents show the enhancement
of F3+-colour centres excitation in the region of metal colloids absorption and the increase is
observed of the emission intensities ratio of F3+ and F2 centers with respect to initial crystals γ-
coloured in identical conditions Emission intensities of both centers under excitation at 458
nm correlate with LiF content These effects which are related to high-quality nanostructures
but at the same time depend strongly on the defect content especially as far as their 1ndash2 ps
nonlinearities are concerned could depend on nanocrystal purity and metal excess collection in
their boundaries regions Our results provide an original contribution to the understanding of
the influence of the nanolayer-by-nanolayer deposition γ-irradiation on these specific
structures and of the metal aggregates on the properties of nanocrystals and nanolayers
1 Introduction
Nano-sized layers films crystals and multilayers play an important role in future technology as they
exhibit different and often unique properties with respect to the initial macroscopic materials [1ndash6]
Film structures with nanocrystals have attracted much interest for the possibility to grow them in their
final position within switching devices detectors efficient dosimeters emitters and solar cells The
possibility of using these nanostructures not only for fundamental studies but also for novel devices
fabrication is stimulating the efforts to control the nanocrystal size shape structure space arranging
as well as their composition and structural defects Unfortunately not only bulk but boundary
(surface) states of nanolayers and nanocrystals affect strongly their properties as their size reduces [1
7] The properties of the nanoelements as prepared and post-growth processed by different methods
3 To whom any correspondence should be addressed
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
ccopy 2010 IOP Publishing Ltd 1
can be affected by the presence of various defects and also by aggregation of impurities and intrinsic
defects to the colloids in the bulk and surface regions related to the used preparation technique
Several physical deposition methods are usable for preparation of thin films and nanostructures such
as laser-assisted electron-beam or thermal evaporation from composite targets and undoped bulks
sequential sputtering or evaporation [1ndash6 8] Ion implantation [9] thermal treatments [10] and
ionising radiation bombardment (combined with special annealing [11ndash14]) are established tools for
metal nanoparticles formation in solids Understanding the structural evolution during the preparation
of nanocomposites can be of great help in understanding how to control the characteristics of the final
products readily
Lithium fluoride is a well-known material which after irradiation by ionizing radiation (electrons
ions γ-rays and X-rays) or laser light is characterized by F-colour centres (CCs) aggregates [3ndash5] and
metal colloids formation sensitive to the content of oxygen hydroxyl and divalent metal ions in initial
crystals [11ndash14] Clusters of F-CCs (lithium colloids) and impurity colloids can be created in the
irradiated regions of LiF and at temperatures where diffusion of the defects is possible [10ndash12] Even
though the actual mechanism of the formation of such colloids is still an open question a lot of
attention was devoted to study optical properties of the crystals and their near surface nanothin layers
containing these metallic aggregates Since thin-film nanolayers and nanocrystals have been studied
only in a limited way in this paper we carried out the following measurements to investigate them
2 Experimental details and measurements
Microstructural and optical characteristics of the investigated samples are summarized in figures 1ndash8
The experimental samples are multilayers and thin-film interferometers (TFIs) with the intermediate
multilayers [15ndash17] Each structure unit is a thin-film nanolayer with a nanocrystal array inside it
(figures 1 2) The geometry of the nanostructures can be tuned by controlling the thicknesses and the
compositions of the ldquosensitizingrdquo and complementary buffer nanolayers Every nanolayer can be
designed of one material [15] and as composition of nanocrystals clusters of two materials [16]
Figure 1 Schematic representation of the periodic multilayer nanostructures with c-oriented
nanocrystals prepared from one (a) two (b) and more than two initial materials (c)
21 Samples preparation
The elaborated samples consist of dielectric (LiF CaF2) orand semiconductor (CdS) nanocrystals
Samples with various ldquosensitizingrdquo nanocrystals are grown on radiation-resistant flat substrates in the
layer-by-layer manner of the reproducing of thin-film nanolayers with defining compositions [15 16]
ldquoSensitizingrdquo nanolayers are prepared with thicknesses equal to nanocrystal sizes [15] and by using
special techniques for nanocrystal ordering [17] The approach presented in this paper can be extended
to fabricate thin-film multilayer structures of a wide range of materials To avoid radiative coloration
thermal evaporation was the preferred fabrication technique Undoped crystals 99999 pure are
used as starting materials The clean substrates were kept at room temperature (RT) on a copper
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
2
holder and the vacuum pressure in the evaporation chamber was about 10ndash6
Torr The films
thicknesses were measured by interference method As-prepared (fresh) samples are kept for seven
days in a dry box before starting the optical measurements in the open atmosphere at RT at about 50
humidity Crystals and films produced in the manner of continuous growth of the result thicknesses
were used as reference samples After the growth some samples were γ-irradiated at RT up to 83 kGy
[19] Self-assembled nanolayers of LiF and CaF2 nanocrystals were used as templates In the case of
CdSeCaF2 CdSCaF2 [20] and LiFCaF2 nanostructures (figure 2) more radiation-resistant crystalline
CaF2 nanolayers were used to promote the c-axis ordering and the size restriction of ldquosensitizingrdquo
CdSe CdS and LiF nanocrystals After thermal evaporation and post-growth γ-colouration spatially
ordered arrays of CCs could be fabricated in the periodic multilayer nanostructures (figure 1b) [6]
(c)
Figure 2 XRD and SEM images of non-irradiated thin-film structures with c-oriented nanocrystals of
cubic phase and defined sizes prepared from LiF (a) CaF2 (b) and LiF and CaF2 initial crystals (c)
22 Samples characterization
The microstructure of thin-film samples is determined by X-ray phase analysis scanning electron
microscopy (SEM) and atomic force microscopy (AFM) The c-axis ordering (texture) analysis of
thin-film nanostructures was performed by means of pole figures and θ-2θ diffraction patterns (figures
2ndash6) A Seifert XRD 3003 PTS four circles diffractometer employing CuKα (λ= 154059 Aring) radiation
was used for pole figure measurements The primary beam was collimated by a 05 mm pinhole and a
1 mm slit was placed in front of the detector The accelerating voltage and current was fixed at 40 kV
and 30 mA respectively Pole figures were recorded varying between 0deg and 360deg with a sampling
interval of 4deg and varying χ between 0deg and 75deg with Δχ=25ordm The acquisition time was 5 seconds X-
ray θ-2θ diffraction pattern were collected by using a Rigaku Geigerflex diffractometer with CuKα
radiation The diffractometer was equipped with a graphite monochromator in order to suppress Kβ
radiation and to increase signal to noise ratio The divergence slit scattering slit and receiving slit
were 05ordm 045deg and 03ordm respectively The measurements were performed with a sampling interval of
005deg and a fixed time of 10 seconds
Optical transmittance (T) and reflectance (R) spectra of samples are measured with a dual beam Cary
500 Scan and a Lambda 19DM Perkin-Elmer spectrophotometers in the spectral range 190ndash3300 nm
(figures 6 8) Optical absorption (OA) (figure 7) is derived from transmittance and is used to estimate
the defects in nanocrystals with respect to initial crystals The photoluminescence (PL) measurements
were carried out by using a Jobin Yvon Fluorolog-3 spectrofluorometer with the front-face detecting
geometry by exciting the samples at the wavelength of 458 nm (M-band LiF) see figures 7bc
Nonlinear properties were detected using a pump-and-probe technique and 3-ps [11ndash15] and 150-fs
laser pulses [3 5] and reported in figure 8 All measurements were performed at RT
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
3
3 Thin-film structures with dielectric nanocrystals
31 Thin-film structures with nanocrystals of one fluoride material
X-ray diffraction (XRD)- SEM- and AFM-results show that non-irradiated multilayers are structures
with definite size of nanocrystals (Final thickness of LiF CaF2 and LiFCaF2 structures is
approximately 65 μm) Presence of (111) and (222) peaks in XRD data of the multilayers indicates
that they have c-axis orientation perpendicular to the substrate surfaces The XRD patterns of LiF and
CaF2 multilayers see figure 2 show intense (111) peaks at 2θ = 387ordm 283ordm and a considerably less
intense (222) peaks at 2θ = 831ordm 585ordm respectively Not-presented here XRD- SEM- and AFM-
results validate the fact that irradiation neither causes a change in the packing nor increases the size of
nanocrystals The (111) peaks prevail in the XRD-patterns of samples and γ-irradiation with the dose
of 83 kGy only improves the crystallinity and the orientation of nanostructures (increase in the
intensities of (111) peaks) The XRD results correlate well with the texture analysis (figures 3ndash5)
(a)
(b) (c)
Figure 3 2d and 3d (111) (200) and (220) LiF pole figures of the non-irradiated LiF
nanostructures (a) Magnification of (111) LiF pole figure in the region χ lt30deg (b)
and -scan of the (200) LiF pole figure demonstrating the in-plane isotropy (c)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
4
In figure 3a two (2d) and three dimensional (3d) (111) (200) and (220) LiF pole figures of the non-
irradiated LiF sample are reported A sharp (111) texture is present The Full Width at Half Maximum
(FWHM) of the pole located at χ=0 in the (111) pole figure is about 6deg and the FWHMs of both (200)
and (220) poles are 8deg This is due to a very low mosaic spread in the growth direction Figure 3b
shows a magnification of the (111) pole figure in the range χ lt30deg The isointensity lines were chosen
in the following way the intensity of the nth line is In = Imax2n The circular shape of the pole indicates
that the in-plane nanocrystal distribution is uniform This hypothesis is supported by the analysis of
the cut of the (200) pole image at χ=55 shown in figure 3c no difference in intensity is observable
varying angle confirming that any preferential in-plane direction does not exist
The (111) (200) and (220) LiF pole figures for the γ-irradiated LiF sample are shown in figure 4 For
this sample perfect (111) texture is presented (a) The FWHM of the (111) (200) and (220) LiF poles
are 5deg 8deg and 7deg respectively The detailed (111) pole in the range χlt30deg (b) and the cut of the (200)
pole figure at χ~55deg (c) are also reported The (111) LiF pole profile is perfectly circular and the (200)
pole -scan is constant indicating a high in-plane isotropy differently from what we observed for non-
irradiated LiF sample in which a low fraction of slightly misoriented nanocrystals can be inferred
(a)
(b) (c)
Figure 4 2d and 3d (111) (200) and (220) LiF pole figures of the γ-irradiated LiF
nanostructures (a) The perfect texture is shown Magnification of (111) LiF pole
figure χ lt30deg (b) and -scan of (200) figure demonstrating in-plane isotropy (c)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
5
It must be emphasized that the difference is very small an analysis of the (111) LiF pole figures
revealed that the integrated intensity of the range χlt10deg (Iχlt10) to the integrated intensity of the total
(111) pole figure (Itotal) ratio varies from 1495 (for the non-irradiated LiF sample) to 1505 (for the
sample γ-irradiated at RT with dose 83 kGy) Conversely the pole maximum is incresed of about 20
in the irradiated sample confirming the effect of the structure improving due to the γ-irradiation
In figure 5 the (111) (400) and (220) CaF2 pole images of non-irradiated CaF2 sample are reported (a)
Also in this case the presence of a good (111) texture is evident The FWHM of (111) (400) and
(220) poles are 5deg 7deg and 7deg The (111) peak profile is circular down to the lowest intensity and no
evidence of peak broadening was observed The pole is misaligned respect to the centre of about 05deg
as can be seen in figure 5b Since the measurement was repeated several times an error in the
mounting of the sample can be excluded A different profile of the -scan performed on the (400) and
(220) poles was recorded (figure 5c) characterised by a weak intensity dependence vs This
behaviour is due to the (111) CaF2 direction not exactly perpendicular to the substrate surface
(a)
(b) (c)
Figure 5 2d and 3d (111) (200) and (220) CaF2 pole figures of non-irradiated
CaF2 nanostructures (a) Magnification of (111) CaF2 pole figure χ lt30deg (b) A
misalignment of ~05deg is present and is consistent with the (400) (220) -scan (c)
Not reported here the poles for the γ-irradiated CaF2 sample revealed the development of more strong
(111) texture The FWHM of the (111) pole is about 4deg indicating a very small mosaic spread
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
6
32 Thin-film structures with nanocrystals of various fluoride materials
To establish the influence of content of LiF nanocrystals with given size on PL spectra of multilayers
two LiFCaF2 structures have been prepared The first LiFCaF2(1) (figure 1b period 1) is the 48-
period structure of 100 nm LiF-nanolayers and 50 nm CaF2-nanolayers The next LiFCaF2(2) is the
24-period structure consisting of 100 nm LiF- and 220 nm CaF2-nanolayers (figure 1b period 2)
(a) LiF (111) LiF (111) CaF2 (111)
Figure 6 3d (111) LiF CaF2 pole images of fresh LiFCaF2(1) (left) and LiFCaF2(2) multilayers
(middle right) (a) XRD patterns of LiFCaF2(2) before (1) after irradiation (2) and fresh LiFCaF2(1)
(3) (b) Transmission spectra of the multilayers and substrate (c) Reflection spectra of LiFCaF2(1) vs
angles of incidence in the range 20ordmndash50ordm (d) The graphs are p-polarized light
Both multilayers were composed of ~100 nm LiF and ~50 nm CaF2 nanocrystals and were c-oriented
structures (figures 6ab) In figure 6a the (111) LiF and CaF2 pole images of as-prepared LiFCaF2(1)
(left) and LiFCaF2(2) samples (middle right) are reported A well-resolved (111) LiF texture is
present on both cases The quantity of used isolines are 128 and the minimal and maximal intensities
in the (111) LiF pole figures are about 910 and 283 cps for the LiFCaF2(1) samples and 450 and
1154 cps for the LiFCaF2(2) samples This is due to the result LiF thickness in the LiFCaF2(1)
sample (45 μm) 27 time larger with respect to the LiFCaF2(2) sample (17 μm) The CaF2 pole image
(figure 6a right) indicates that the preferential nanocrystal orientation is (111) direction The
crystallinity and (111) texture improving for the γ-irradiated LiFCaF2 samples is supported by the
XRD patterns shown in figure 6b strong difference is observable between the data measured for
LiFCaF2(2) before (curve 1) and after γ-irradiation at RT with dose 83 kGy (curve 2)
High-reflectivity and transmissivity bands are provided by the LiFCaF2 structures (figure 2c) Spectral
positions of the bands were not changed after γ-irradiation but were sensitive to the polarization state
and angle of incidence of light see figure 2d The LiFCaF2 structures covered at the surface by CaF2
nanolayers are more mechanically stable and resistant to external influences than LiF nanostructures
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
7
33 Optical absorption features of non-irradiated thin-film structures
OA spectra of non-irradiated LiF nanostructures and initial crystals with small content of Mg2+
O2ndash
and OHndash ions [13] show well-resolved absorption of Mg
2+ colloids [11 12] (figure 7a) (The non-
irradiated and γ-irradiated substrates remain non-absorbing in the above spectral range) According to
the literature besides Mg colloids with the absorption band peaked at 44ndash46 eV the low-wavelength
absorption band at 36ndash41 eV related to the formation of more large Mg colloids or intrinsic Li
colloids [11 12] are reliably distinguished in non-irradiated LiF nanostructures (figure 7a) [21] and
initial crystals γ-irradiated with various doses and bleached by annealing after irradiation (figure 7a
insert) [13 14]
Figure 7 OA spectra of non-coloured (a) and PL spectra of γ-coloured nano (bold curve) and bulk
(solid curve) crystalline structures (b) and the structures with various LiF contents (c)
34 PL spectra of the irradiated thin-film structures
Non-presented here PL spectra of γ-irradiated CaF2 nanocrystals are composed of the reference 425
nm band excited at the wavelength of 370 nm The PL spectra of initial LiF crystal LiF and LiFCaF2
nanostructures having the same size of LiF nanocrystals and irradiated in analogous conditions are
given in figures 7bc In comparison with the initial crystals an increase of F3+-CCs excitation in the
region of Mg colloids absorption in nanostructures is observed together with an enhanced emission in
the green region with respect to the red one for γ-irradiated film structures (figures 7b) The
normalized emission spectra of nanostructures with various LiF content (bold) have the same shape
the F3+ photoluminescence band intensity at λmax = 538 nm increases of the same factor in comparison
with the F2 emission at 670 nm with respect to the spectrum of the crystal (solid curve) The PL
spectra show an increase (correlated with LiF nanocrystal content) of the intensities of F3+ and F2
bands (figure 7c) These results could be explained by the high structural and optical qualities of these
nanostructures (the overall emission is proportional to the quantity of luminescent LiF nanocrystals)
and by the nanocrystal purity with metal excess collection in their boundaries regions [22]
4 Thin-film structures with semiconductor and dielectric nanocrystals We measured nonlinear optical (NLO) effects for the reference films (figure 8a curve 1) elaborated
multilayers (figure 8a curves 2 3) and specially-elaborated multipeak TFIs containing c-oriented
cubic CdS nanocrystals of defined sizes as reported in figure 8 Sample 3 and TFIs intermediate layers
are composite film structures with semiconductor (CdS) and dielectric (CaF2) nanocrystals (figure 1c)
Separation of the transient shift and absorption saturation in TFIs gives us the features of both effects
Characteristic 1ndash2 ps decay of the shift confirms the metal clusters nature of the effect [23 24]
Maximal NLO effects in nanocrystals are increased with size reduction and are enhanced by extra
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
8
excitation power pulse durability [20 22] and γ-irradiation [19] These effects can be explained by
accumulation of colloids and electrons at nanocrystal boundaries
Figure 8 NLO characteristics detected for (a) reference films (1) multilayers (2 3) (b) multipeak
TFIs with c-oriented cubic CdS nanocrystals of defined sizes (c) Transmission spectra of the TFI
before (B) and at time of excitation (time delay between the excitation and registration is zero) (A)
Impurities and nonstoichiometric excess tend to be expelled from the small crystalline core as the
distance a defect or impurity must move to reach the surface of a nanocrystal is very small
Self-purification of the nanocrystals can be explained through technological arguments and is an
intrinsic property of defects in nanocrystals prepared by the methods of alternative deposition of
nanolayers with thicknesses 150ndash10 nm Post-growth thermal treatments ionising radiation
bombardment and light irradiation of the nanocrystals are the next tools for the nanocrystal
purification metal colloids formation and the nanocrystal properties modification
5 Conclusion
The c-axis highly oriented thin-film multilayer structures composed of dielectric (LiF CaF2) and
semiconductor (CdS) nanocrystals prepared by thermal evaporation show enhanced photo-response
which is related to high-quality nanocrystals but at the same time depends strongly on the defect
content especially as far as their 1ndash2 ps nonlinearities are concerned Critical factors are nanocrystal
purity as well as metal impurities and nonstoichiometric excess collection in their boundaries regions
The nanostructures (more high-quality than original bulk structures) can be part of efficient emitting
elements detectors and modulators of light as well as a novel type of dosimeters Such optically
stimulated luminescence dosimeters (integrable with SiO2OH fibres) provide capability for remote
monitoring radiation locations which are difficult to access and hazardous These devices are relatively
simple small in size cheap in production and have low power consumption Moreover they are also
suitable for space radiation dose exploration In addition they can be used in other radiation
measurements and have interesting perspectives in the case of periodical nanostructures composed of
the nanolayers of CdS and LiF nanocrystals with high-contrast indices of refraction (figure 1c)
Acknowledgments
The authors are indebted to O Bilan A Pace and V Gremenok for their help in irradiation and
microstructure testing of the samples Many thanks are due to M A Vincenti S Tikhomirov and O
Buganov for their assistance during PL and NLO experiments This work is supported by the
Belarusian National Program for Crystalline and Molecular Structures Research Project CMS-35 and
by the grants of the ENEA Fellowships Programme (Frascati Research Center Rome Italy)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
9
6 References
[1] Poole Ch and Owens F 2003 Introduction to Nanotechnology (New York John Wiley)
[2] Goncharova O 1994 Semiconductor microcrystallites in thin-film matrix fabrication methods
optical properties and application prospects New Materials for Thin Film Functional
Electronic-Technological Components ed V Labunov (Minsk Nauka i Tekhnika) chapter 6
pp 99ndash176
[3] Baldacchini G Cremona M dAuria G Martelli S Montereali R M Montecchi M Burattini E
Grilli A and Raco A 1996 Nucl Instr Meth B 116 447ndash51
[4] Montereali R M 2002 Point Defects in Thin Insulating films of Lithium Fluoride for Optical
Microsystems Ferroelectric and Dielectric Thin Films (Handbook of Thin Films Materials
vol 3) ed H S Nalwa (New York Academic Press) chapter 7 pp 399ndash431
[5] Kumar M et al 2005 J Phys D Appl Phys 38 637ndash41
[6] Goncharova O 2005 Microstructure and properties of periodic multilayer thin-film structures
with nanocrystals Advances in Spectroscopy for Lasers and Sensing Proc NATO Advanced
Study Institute (Erice Sicily Italy 6ndash21 June 2005) (NATO Science Series II
Mathematics Physics and Chemistry vol 231) ed B Di Bartolo and O Forte (Berlin
Springer) p 556
[7] Goncharova O Karpushko F V and Sinitsyn G V 1983 Technical Physics 28 1142ndash44
[8] Pulker H K 1979 Appl Optics 18 1969ndash77
[9] Wang Y H Lu J D Wang R W Mao Y L and Cheng Y G 2008 Vacuum 82 1220ndash23
[10] Bryukvina L I Ermolaeva E A Pidgurskii S N Suvorova L F and Khulugurov V M 2006 Phys
Sol State 48 68ndash72
[11] Schwartz K K Lyushina A F and Vitol A Ya 1969 Sov Phys Sol State 11 1885ndash90
[12] Lushchik A Lushchik Ch Schwartz K Vasilchenko E Papaleo R Sorokin M Volkov A E
Neumann R and Trautmann C 2007 Phys Rev B 76 054114
[13] Baldacchini G Goncharova O Kalinov V S Montereali R M Nichelatti E Vincenti A and
Voitovich A P 2007 Phys Status Solidi C 4 744ndash48
[14] Baldacchini G Goncharova O Kalinov V S Montereali R M Vincenti A and Voitovich A P
2007 Phys Status Solidi C 4 1134ndash38
[15] Goncharova O and Demin V 1993 Photosensitive resistive nonlinear optical thin-film
heterostructures RF Patent 2089656
[16] Goncharova O and Demin V 1994 Photosensitive resistive nonlinear optical composite films
RF Patent 2103846
[17] Goncharova O and Demin V 1994 Narrow-band thin-film FabryndashPerot interferometer RF
Patent 2078358
[18] Goncharova O 1998 Light-induced ultrafast bleaching in films of different arranging of
semiconductor nanocrystals materials Proc Int Conf on Coherent and Nonlinear Optics
(Moscow Russia 29 June ndash 3 July 1998) (Moscow Moscow State University Press) p 246
[19] Goncharova O Kalinov V and Voitovich A 2004 Radiat Meas 38 775ndash79
[20] Goncharova O 1996 Picosecond all-optical switching in thin-film FabryndashPerot interferometers
and cavityless devices Notes and Perspectives of Nonlinear Optics (Nonlinear Optics vol 3)
ed O Keller (London World Scientific) pp 636ndash42
[21] Goncharova O and Gremenok V 2007 Comparative study of electronic structure of thin film
nanocrystals prepared by low-temperature vacuum deposition Proc Int Conf CLEOEurope-
2007 (Munich Germany 17ndash22 June 2007) p 1-1
[22] Goncharova O Montereali R M and Baldacchini G 2008 Abstr Int Conf ICL-2008 Lyon
France 7ndash11 July 2008) p 160
[23] Goncharova O 1996 Studies on a Nature of the Picosecond Transient Absorption in Thin Films
Activated by Semiconductor or Metal Nanocrystals Proc Int Conf EQEC-1996 (Hamburg
Germany 8ndash13 Sept 1996) p 87
[24] Z Lu and K Zhu 2008 J Phys B At Mol Opt Phys 41 185503ndash09
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
10
can be affected by the presence of various defects and also by aggregation of impurities and intrinsic
defects to the colloids in the bulk and surface regions related to the used preparation technique
Several physical deposition methods are usable for preparation of thin films and nanostructures such
as laser-assisted electron-beam or thermal evaporation from composite targets and undoped bulks
sequential sputtering or evaporation [1ndash6 8] Ion implantation [9] thermal treatments [10] and
ionising radiation bombardment (combined with special annealing [11ndash14]) are established tools for
metal nanoparticles formation in solids Understanding the structural evolution during the preparation
of nanocomposites can be of great help in understanding how to control the characteristics of the final
products readily
Lithium fluoride is a well-known material which after irradiation by ionizing radiation (electrons
ions γ-rays and X-rays) or laser light is characterized by F-colour centres (CCs) aggregates [3ndash5] and
metal colloids formation sensitive to the content of oxygen hydroxyl and divalent metal ions in initial
crystals [11ndash14] Clusters of F-CCs (lithium colloids) and impurity colloids can be created in the
irradiated regions of LiF and at temperatures where diffusion of the defects is possible [10ndash12] Even
though the actual mechanism of the formation of such colloids is still an open question a lot of
attention was devoted to study optical properties of the crystals and their near surface nanothin layers
containing these metallic aggregates Since thin-film nanolayers and nanocrystals have been studied
only in a limited way in this paper we carried out the following measurements to investigate them
2 Experimental details and measurements
Microstructural and optical characteristics of the investigated samples are summarized in figures 1ndash8
The experimental samples are multilayers and thin-film interferometers (TFIs) with the intermediate
multilayers [15ndash17] Each structure unit is a thin-film nanolayer with a nanocrystal array inside it
(figures 1 2) The geometry of the nanostructures can be tuned by controlling the thicknesses and the
compositions of the ldquosensitizingrdquo and complementary buffer nanolayers Every nanolayer can be
designed of one material [15] and as composition of nanocrystals clusters of two materials [16]
Figure 1 Schematic representation of the periodic multilayer nanostructures with c-oriented
nanocrystals prepared from one (a) two (b) and more than two initial materials (c)
21 Samples preparation
The elaborated samples consist of dielectric (LiF CaF2) orand semiconductor (CdS) nanocrystals
Samples with various ldquosensitizingrdquo nanocrystals are grown on radiation-resistant flat substrates in the
layer-by-layer manner of the reproducing of thin-film nanolayers with defining compositions [15 16]
ldquoSensitizingrdquo nanolayers are prepared with thicknesses equal to nanocrystal sizes [15] and by using
special techniques for nanocrystal ordering [17] The approach presented in this paper can be extended
to fabricate thin-film multilayer structures of a wide range of materials To avoid radiative coloration
thermal evaporation was the preferred fabrication technique Undoped crystals 99999 pure are
used as starting materials The clean substrates were kept at room temperature (RT) on a copper
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
2
holder and the vacuum pressure in the evaporation chamber was about 10ndash6
Torr The films
thicknesses were measured by interference method As-prepared (fresh) samples are kept for seven
days in a dry box before starting the optical measurements in the open atmosphere at RT at about 50
humidity Crystals and films produced in the manner of continuous growth of the result thicknesses
were used as reference samples After the growth some samples were γ-irradiated at RT up to 83 kGy
[19] Self-assembled nanolayers of LiF and CaF2 nanocrystals were used as templates In the case of
CdSeCaF2 CdSCaF2 [20] and LiFCaF2 nanostructures (figure 2) more radiation-resistant crystalline
CaF2 nanolayers were used to promote the c-axis ordering and the size restriction of ldquosensitizingrdquo
CdSe CdS and LiF nanocrystals After thermal evaporation and post-growth γ-colouration spatially
ordered arrays of CCs could be fabricated in the periodic multilayer nanostructures (figure 1b) [6]
(c)
Figure 2 XRD and SEM images of non-irradiated thin-film structures with c-oriented nanocrystals of
cubic phase and defined sizes prepared from LiF (a) CaF2 (b) and LiF and CaF2 initial crystals (c)
22 Samples characterization
The microstructure of thin-film samples is determined by X-ray phase analysis scanning electron
microscopy (SEM) and atomic force microscopy (AFM) The c-axis ordering (texture) analysis of
thin-film nanostructures was performed by means of pole figures and θ-2θ diffraction patterns (figures
2ndash6) A Seifert XRD 3003 PTS four circles diffractometer employing CuKα (λ= 154059 Aring) radiation
was used for pole figure measurements The primary beam was collimated by a 05 mm pinhole and a
1 mm slit was placed in front of the detector The accelerating voltage and current was fixed at 40 kV
and 30 mA respectively Pole figures were recorded varying between 0deg and 360deg with a sampling
interval of 4deg and varying χ between 0deg and 75deg with Δχ=25ordm The acquisition time was 5 seconds X-
ray θ-2θ diffraction pattern were collected by using a Rigaku Geigerflex diffractometer with CuKα
radiation The diffractometer was equipped with a graphite monochromator in order to suppress Kβ
radiation and to increase signal to noise ratio The divergence slit scattering slit and receiving slit
were 05ordm 045deg and 03ordm respectively The measurements were performed with a sampling interval of
005deg and a fixed time of 10 seconds
Optical transmittance (T) and reflectance (R) spectra of samples are measured with a dual beam Cary
500 Scan and a Lambda 19DM Perkin-Elmer spectrophotometers in the spectral range 190ndash3300 nm
(figures 6 8) Optical absorption (OA) (figure 7) is derived from transmittance and is used to estimate
the defects in nanocrystals with respect to initial crystals The photoluminescence (PL) measurements
were carried out by using a Jobin Yvon Fluorolog-3 spectrofluorometer with the front-face detecting
geometry by exciting the samples at the wavelength of 458 nm (M-band LiF) see figures 7bc
Nonlinear properties were detected using a pump-and-probe technique and 3-ps [11ndash15] and 150-fs
laser pulses [3 5] and reported in figure 8 All measurements were performed at RT
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
3
3 Thin-film structures with dielectric nanocrystals
31 Thin-film structures with nanocrystals of one fluoride material
X-ray diffraction (XRD)- SEM- and AFM-results show that non-irradiated multilayers are structures
with definite size of nanocrystals (Final thickness of LiF CaF2 and LiFCaF2 structures is
approximately 65 μm) Presence of (111) and (222) peaks in XRD data of the multilayers indicates
that they have c-axis orientation perpendicular to the substrate surfaces The XRD patterns of LiF and
CaF2 multilayers see figure 2 show intense (111) peaks at 2θ = 387ordm 283ordm and a considerably less
intense (222) peaks at 2θ = 831ordm 585ordm respectively Not-presented here XRD- SEM- and AFM-
results validate the fact that irradiation neither causes a change in the packing nor increases the size of
nanocrystals The (111) peaks prevail in the XRD-patterns of samples and γ-irradiation with the dose
of 83 kGy only improves the crystallinity and the orientation of nanostructures (increase in the
intensities of (111) peaks) The XRD results correlate well with the texture analysis (figures 3ndash5)
(a)
(b) (c)
Figure 3 2d and 3d (111) (200) and (220) LiF pole figures of the non-irradiated LiF
nanostructures (a) Magnification of (111) LiF pole figure in the region χ lt30deg (b)
and -scan of the (200) LiF pole figure demonstrating the in-plane isotropy (c)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
4
In figure 3a two (2d) and three dimensional (3d) (111) (200) and (220) LiF pole figures of the non-
irradiated LiF sample are reported A sharp (111) texture is present The Full Width at Half Maximum
(FWHM) of the pole located at χ=0 in the (111) pole figure is about 6deg and the FWHMs of both (200)
and (220) poles are 8deg This is due to a very low mosaic spread in the growth direction Figure 3b
shows a magnification of the (111) pole figure in the range χ lt30deg The isointensity lines were chosen
in the following way the intensity of the nth line is In = Imax2n The circular shape of the pole indicates
that the in-plane nanocrystal distribution is uniform This hypothesis is supported by the analysis of
the cut of the (200) pole image at χ=55 shown in figure 3c no difference in intensity is observable
varying angle confirming that any preferential in-plane direction does not exist
The (111) (200) and (220) LiF pole figures for the γ-irradiated LiF sample are shown in figure 4 For
this sample perfect (111) texture is presented (a) The FWHM of the (111) (200) and (220) LiF poles
are 5deg 8deg and 7deg respectively The detailed (111) pole in the range χlt30deg (b) and the cut of the (200)
pole figure at χ~55deg (c) are also reported The (111) LiF pole profile is perfectly circular and the (200)
pole -scan is constant indicating a high in-plane isotropy differently from what we observed for non-
irradiated LiF sample in which a low fraction of slightly misoriented nanocrystals can be inferred
(a)
(b) (c)
Figure 4 2d and 3d (111) (200) and (220) LiF pole figures of the γ-irradiated LiF
nanostructures (a) The perfect texture is shown Magnification of (111) LiF pole
figure χ lt30deg (b) and -scan of (200) figure demonstrating in-plane isotropy (c)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
5
It must be emphasized that the difference is very small an analysis of the (111) LiF pole figures
revealed that the integrated intensity of the range χlt10deg (Iχlt10) to the integrated intensity of the total
(111) pole figure (Itotal) ratio varies from 1495 (for the non-irradiated LiF sample) to 1505 (for the
sample γ-irradiated at RT with dose 83 kGy) Conversely the pole maximum is incresed of about 20
in the irradiated sample confirming the effect of the structure improving due to the γ-irradiation
In figure 5 the (111) (400) and (220) CaF2 pole images of non-irradiated CaF2 sample are reported (a)
Also in this case the presence of a good (111) texture is evident The FWHM of (111) (400) and
(220) poles are 5deg 7deg and 7deg The (111) peak profile is circular down to the lowest intensity and no
evidence of peak broadening was observed The pole is misaligned respect to the centre of about 05deg
as can be seen in figure 5b Since the measurement was repeated several times an error in the
mounting of the sample can be excluded A different profile of the -scan performed on the (400) and
(220) poles was recorded (figure 5c) characterised by a weak intensity dependence vs This
behaviour is due to the (111) CaF2 direction not exactly perpendicular to the substrate surface
(a)
(b) (c)
Figure 5 2d and 3d (111) (200) and (220) CaF2 pole figures of non-irradiated
CaF2 nanostructures (a) Magnification of (111) CaF2 pole figure χ lt30deg (b) A
misalignment of ~05deg is present and is consistent with the (400) (220) -scan (c)
Not reported here the poles for the γ-irradiated CaF2 sample revealed the development of more strong
(111) texture The FWHM of the (111) pole is about 4deg indicating a very small mosaic spread
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
6
32 Thin-film structures with nanocrystals of various fluoride materials
To establish the influence of content of LiF nanocrystals with given size on PL spectra of multilayers
two LiFCaF2 structures have been prepared The first LiFCaF2(1) (figure 1b period 1) is the 48-
period structure of 100 nm LiF-nanolayers and 50 nm CaF2-nanolayers The next LiFCaF2(2) is the
24-period structure consisting of 100 nm LiF- and 220 nm CaF2-nanolayers (figure 1b period 2)
(a) LiF (111) LiF (111) CaF2 (111)
Figure 6 3d (111) LiF CaF2 pole images of fresh LiFCaF2(1) (left) and LiFCaF2(2) multilayers
(middle right) (a) XRD patterns of LiFCaF2(2) before (1) after irradiation (2) and fresh LiFCaF2(1)
(3) (b) Transmission spectra of the multilayers and substrate (c) Reflection spectra of LiFCaF2(1) vs
angles of incidence in the range 20ordmndash50ordm (d) The graphs are p-polarized light
Both multilayers were composed of ~100 nm LiF and ~50 nm CaF2 nanocrystals and were c-oriented
structures (figures 6ab) In figure 6a the (111) LiF and CaF2 pole images of as-prepared LiFCaF2(1)
(left) and LiFCaF2(2) samples (middle right) are reported A well-resolved (111) LiF texture is
present on both cases The quantity of used isolines are 128 and the minimal and maximal intensities
in the (111) LiF pole figures are about 910 and 283 cps for the LiFCaF2(1) samples and 450 and
1154 cps for the LiFCaF2(2) samples This is due to the result LiF thickness in the LiFCaF2(1)
sample (45 μm) 27 time larger with respect to the LiFCaF2(2) sample (17 μm) The CaF2 pole image
(figure 6a right) indicates that the preferential nanocrystal orientation is (111) direction The
crystallinity and (111) texture improving for the γ-irradiated LiFCaF2 samples is supported by the
XRD patterns shown in figure 6b strong difference is observable between the data measured for
LiFCaF2(2) before (curve 1) and after γ-irradiation at RT with dose 83 kGy (curve 2)
High-reflectivity and transmissivity bands are provided by the LiFCaF2 structures (figure 2c) Spectral
positions of the bands were not changed after γ-irradiation but were sensitive to the polarization state
and angle of incidence of light see figure 2d The LiFCaF2 structures covered at the surface by CaF2
nanolayers are more mechanically stable and resistant to external influences than LiF nanostructures
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
7
33 Optical absorption features of non-irradiated thin-film structures
OA spectra of non-irradiated LiF nanostructures and initial crystals with small content of Mg2+
O2ndash
and OHndash ions [13] show well-resolved absorption of Mg
2+ colloids [11 12] (figure 7a) (The non-
irradiated and γ-irradiated substrates remain non-absorbing in the above spectral range) According to
the literature besides Mg colloids with the absorption band peaked at 44ndash46 eV the low-wavelength
absorption band at 36ndash41 eV related to the formation of more large Mg colloids or intrinsic Li
colloids [11 12] are reliably distinguished in non-irradiated LiF nanostructures (figure 7a) [21] and
initial crystals γ-irradiated with various doses and bleached by annealing after irradiation (figure 7a
insert) [13 14]
Figure 7 OA spectra of non-coloured (a) and PL spectra of γ-coloured nano (bold curve) and bulk
(solid curve) crystalline structures (b) and the structures with various LiF contents (c)
34 PL spectra of the irradiated thin-film structures
Non-presented here PL spectra of γ-irradiated CaF2 nanocrystals are composed of the reference 425
nm band excited at the wavelength of 370 nm The PL spectra of initial LiF crystal LiF and LiFCaF2
nanostructures having the same size of LiF nanocrystals and irradiated in analogous conditions are
given in figures 7bc In comparison with the initial crystals an increase of F3+-CCs excitation in the
region of Mg colloids absorption in nanostructures is observed together with an enhanced emission in
the green region with respect to the red one for γ-irradiated film structures (figures 7b) The
normalized emission spectra of nanostructures with various LiF content (bold) have the same shape
the F3+ photoluminescence band intensity at λmax = 538 nm increases of the same factor in comparison
with the F2 emission at 670 nm with respect to the spectrum of the crystal (solid curve) The PL
spectra show an increase (correlated with LiF nanocrystal content) of the intensities of F3+ and F2
bands (figure 7c) These results could be explained by the high structural and optical qualities of these
nanostructures (the overall emission is proportional to the quantity of luminescent LiF nanocrystals)
and by the nanocrystal purity with metal excess collection in their boundaries regions [22]
4 Thin-film structures with semiconductor and dielectric nanocrystals We measured nonlinear optical (NLO) effects for the reference films (figure 8a curve 1) elaborated
multilayers (figure 8a curves 2 3) and specially-elaborated multipeak TFIs containing c-oriented
cubic CdS nanocrystals of defined sizes as reported in figure 8 Sample 3 and TFIs intermediate layers
are composite film structures with semiconductor (CdS) and dielectric (CaF2) nanocrystals (figure 1c)
Separation of the transient shift and absorption saturation in TFIs gives us the features of both effects
Characteristic 1ndash2 ps decay of the shift confirms the metal clusters nature of the effect [23 24]
Maximal NLO effects in nanocrystals are increased with size reduction and are enhanced by extra
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
8
excitation power pulse durability [20 22] and γ-irradiation [19] These effects can be explained by
accumulation of colloids and electrons at nanocrystal boundaries
Figure 8 NLO characteristics detected for (a) reference films (1) multilayers (2 3) (b) multipeak
TFIs with c-oriented cubic CdS nanocrystals of defined sizes (c) Transmission spectra of the TFI
before (B) and at time of excitation (time delay between the excitation and registration is zero) (A)
Impurities and nonstoichiometric excess tend to be expelled from the small crystalline core as the
distance a defect or impurity must move to reach the surface of a nanocrystal is very small
Self-purification of the nanocrystals can be explained through technological arguments and is an
intrinsic property of defects in nanocrystals prepared by the methods of alternative deposition of
nanolayers with thicknesses 150ndash10 nm Post-growth thermal treatments ionising radiation
bombardment and light irradiation of the nanocrystals are the next tools for the nanocrystal
purification metal colloids formation and the nanocrystal properties modification
5 Conclusion
The c-axis highly oriented thin-film multilayer structures composed of dielectric (LiF CaF2) and
semiconductor (CdS) nanocrystals prepared by thermal evaporation show enhanced photo-response
which is related to high-quality nanocrystals but at the same time depends strongly on the defect
content especially as far as their 1ndash2 ps nonlinearities are concerned Critical factors are nanocrystal
purity as well as metal impurities and nonstoichiometric excess collection in their boundaries regions
The nanostructures (more high-quality than original bulk structures) can be part of efficient emitting
elements detectors and modulators of light as well as a novel type of dosimeters Such optically
stimulated luminescence dosimeters (integrable with SiO2OH fibres) provide capability for remote
monitoring radiation locations which are difficult to access and hazardous These devices are relatively
simple small in size cheap in production and have low power consumption Moreover they are also
suitable for space radiation dose exploration In addition they can be used in other radiation
measurements and have interesting perspectives in the case of periodical nanostructures composed of
the nanolayers of CdS and LiF nanocrystals with high-contrast indices of refraction (figure 1c)
Acknowledgments
The authors are indebted to O Bilan A Pace and V Gremenok for their help in irradiation and
microstructure testing of the samples Many thanks are due to M A Vincenti S Tikhomirov and O
Buganov for their assistance during PL and NLO experiments This work is supported by the
Belarusian National Program for Crystalline and Molecular Structures Research Project CMS-35 and
by the grants of the ENEA Fellowships Programme (Frascati Research Center Rome Italy)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
9
6 References
[1] Poole Ch and Owens F 2003 Introduction to Nanotechnology (New York John Wiley)
[2] Goncharova O 1994 Semiconductor microcrystallites in thin-film matrix fabrication methods
optical properties and application prospects New Materials for Thin Film Functional
Electronic-Technological Components ed V Labunov (Minsk Nauka i Tekhnika) chapter 6
pp 99ndash176
[3] Baldacchini G Cremona M dAuria G Martelli S Montereali R M Montecchi M Burattini E
Grilli A and Raco A 1996 Nucl Instr Meth B 116 447ndash51
[4] Montereali R M 2002 Point Defects in Thin Insulating films of Lithium Fluoride for Optical
Microsystems Ferroelectric and Dielectric Thin Films (Handbook of Thin Films Materials
vol 3) ed H S Nalwa (New York Academic Press) chapter 7 pp 399ndash431
[5] Kumar M et al 2005 J Phys D Appl Phys 38 637ndash41
[6] Goncharova O 2005 Microstructure and properties of periodic multilayer thin-film structures
with nanocrystals Advances in Spectroscopy for Lasers and Sensing Proc NATO Advanced
Study Institute (Erice Sicily Italy 6ndash21 June 2005) (NATO Science Series II
Mathematics Physics and Chemistry vol 231) ed B Di Bartolo and O Forte (Berlin
Springer) p 556
[7] Goncharova O Karpushko F V and Sinitsyn G V 1983 Technical Physics 28 1142ndash44
[8] Pulker H K 1979 Appl Optics 18 1969ndash77
[9] Wang Y H Lu J D Wang R W Mao Y L and Cheng Y G 2008 Vacuum 82 1220ndash23
[10] Bryukvina L I Ermolaeva E A Pidgurskii S N Suvorova L F and Khulugurov V M 2006 Phys
Sol State 48 68ndash72
[11] Schwartz K K Lyushina A F and Vitol A Ya 1969 Sov Phys Sol State 11 1885ndash90
[12] Lushchik A Lushchik Ch Schwartz K Vasilchenko E Papaleo R Sorokin M Volkov A E
Neumann R and Trautmann C 2007 Phys Rev B 76 054114
[13] Baldacchini G Goncharova O Kalinov V S Montereali R M Nichelatti E Vincenti A and
Voitovich A P 2007 Phys Status Solidi C 4 744ndash48
[14] Baldacchini G Goncharova O Kalinov V S Montereali R M Vincenti A and Voitovich A P
2007 Phys Status Solidi C 4 1134ndash38
[15] Goncharova O and Demin V 1993 Photosensitive resistive nonlinear optical thin-film
heterostructures RF Patent 2089656
[16] Goncharova O and Demin V 1994 Photosensitive resistive nonlinear optical composite films
RF Patent 2103846
[17] Goncharova O and Demin V 1994 Narrow-band thin-film FabryndashPerot interferometer RF
Patent 2078358
[18] Goncharova O 1998 Light-induced ultrafast bleaching in films of different arranging of
semiconductor nanocrystals materials Proc Int Conf on Coherent and Nonlinear Optics
(Moscow Russia 29 June ndash 3 July 1998) (Moscow Moscow State University Press) p 246
[19] Goncharova O Kalinov V and Voitovich A 2004 Radiat Meas 38 775ndash79
[20] Goncharova O 1996 Picosecond all-optical switching in thin-film FabryndashPerot interferometers
and cavityless devices Notes and Perspectives of Nonlinear Optics (Nonlinear Optics vol 3)
ed O Keller (London World Scientific) pp 636ndash42
[21] Goncharova O and Gremenok V 2007 Comparative study of electronic structure of thin film
nanocrystals prepared by low-temperature vacuum deposition Proc Int Conf CLEOEurope-
2007 (Munich Germany 17ndash22 June 2007) p 1-1
[22] Goncharova O Montereali R M and Baldacchini G 2008 Abstr Int Conf ICL-2008 Lyon
France 7ndash11 July 2008) p 160
[23] Goncharova O 1996 Studies on a Nature of the Picosecond Transient Absorption in Thin Films
Activated by Semiconductor or Metal Nanocrystals Proc Int Conf EQEC-1996 (Hamburg
Germany 8ndash13 Sept 1996) p 87
[24] Z Lu and K Zhu 2008 J Phys B At Mol Opt Phys 41 185503ndash09
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
10
holder and the vacuum pressure in the evaporation chamber was about 10ndash6
Torr The films
thicknesses were measured by interference method As-prepared (fresh) samples are kept for seven
days in a dry box before starting the optical measurements in the open atmosphere at RT at about 50
humidity Crystals and films produced in the manner of continuous growth of the result thicknesses
were used as reference samples After the growth some samples were γ-irradiated at RT up to 83 kGy
[19] Self-assembled nanolayers of LiF and CaF2 nanocrystals were used as templates In the case of
CdSeCaF2 CdSCaF2 [20] and LiFCaF2 nanostructures (figure 2) more radiation-resistant crystalline
CaF2 nanolayers were used to promote the c-axis ordering and the size restriction of ldquosensitizingrdquo
CdSe CdS and LiF nanocrystals After thermal evaporation and post-growth γ-colouration spatially
ordered arrays of CCs could be fabricated in the periodic multilayer nanostructures (figure 1b) [6]
(c)
Figure 2 XRD and SEM images of non-irradiated thin-film structures with c-oriented nanocrystals of
cubic phase and defined sizes prepared from LiF (a) CaF2 (b) and LiF and CaF2 initial crystals (c)
22 Samples characterization
The microstructure of thin-film samples is determined by X-ray phase analysis scanning electron
microscopy (SEM) and atomic force microscopy (AFM) The c-axis ordering (texture) analysis of
thin-film nanostructures was performed by means of pole figures and θ-2θ diffraction patterns (figures
2ndash6) A Seifert XRD 3003 PTS four circles diffractometer employing CuKα (λ= 154059 Aring) radiation
was used for pole figure measurements The primary beam was collimated by a 05 mm pinhole and a
1 mm slit was placed in front of the detector The accelerating voltage and current was fixed at 40 kV
and 30 mA respectively Pole figures were recorded varying between 0deg and 360deg with a sampling
interval of 4deg and varying χ between 0deg and 75deg with Δχ=25ordm The acquisition time was 5 seconds X-
ray θ-2θ diffraction pattern were collected by using a Rigaku Geigerflex diffractometer with CuKα
radiation The diffractometer was equipped with a graphite monochromator in order to suppress Kβ
radiation and to increase signal to noise ratio The divergence slit scattering slit and receiving slit
were 05ordm 045deg and 03ordm respectively The measurements were performed with a sampling interval of
005deg and a fixed time of 10 seconds
Optical transmittance (T) and reflectance (R) spectra of samples are measured with a dual beam Cary
500 Scan and a Lambda 19DM Perkin-Elmer spectrophotometers in the spectral range 190ndash3300 nm
(figures 6 8) Optical absorption (OA) (figure 7) is derived from transmittance and is used to estimate
the defects in nanocrystals with respect to initial crystals The photoluminescence (PL) measurements
were carried out by using a Jobin Yvon Fluorolog-3 spectrofluorometer with the front-face detecting
geometry by exciting the samples at the wavelength of 458 nm (M-band LiF) see figures 7bc
Nonlinear properties were detected using a pump-and-probe technique and 3-ps [11ndash15] and 150-fs
laser pulses [3 5] and reported in figure 8 All measurements were performed at RT
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
3
3 Thin-film structures with dielectric nanocrystals
31 Thin-film structures with nanocrystals of one fluoride material
X-ray diffraction (XRD)- SEM- and AFM-results show that non-irradiated multilayers are structures
with definite size of nanocrystals (Final thickness of LiF CaF2 and LiFCaF2 structures is
approximately 65 μm) Presence of (111) and (222) peaks in XRD data of the multilayers indicates
that they have c-axis orientation perpendicular to the substrate surfaces The XRD patterns of LiF and
CaF2 multilayers see figure 2 show intense (111) peaks at 2θ = 387ordm 283ordm and a considerably less
intense (222) peaks at 2θ = 831ordm 585ordm respectively Not-presented here XRD- SEM- and AFM-
results validate the fact that irradiation neither causes a change in the packing nor increases the size of
nanocrystals The (111) peaks prevail in the XRD-patterns of samples and γ-irradiation with the dose
of 83 kGy only improves the crystallinity and the orientation of nanostructures (increase in the
intensities of (111) peaks) The XRD results correlate well with the texture analysis (figures 3ndash5)
(a)
(b) (c)
Figure 3 2d and 3d (111) (200) and (220) LiF pole figures of the non-irradiated LiF
nanostructures (a) Magnification of (111) LiF pole figure in the region χ lt30deg (b)
and -scan of the (200) LiF pole figure demonstrating the in-plane isotropy (c)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
4
In figure 3a two (2d) and three dimensional (3d) (111) (200) and (220) LiF pole figures of the non-
irradiated LiF sample are reported A sharp (111) texture is present The Full Width at Half Maximum
(FWHM) of the pole located at χ=0 in the (111) pole figure is about 6deg and the FWHMs of both (200)
and (220) poles are 8deg This is due to a very low mosaic spread in the growth direction Figure 3b
shows a magnification of the (111) pole figure in the range χ lt30deg The isointensity lines were chosen
in the following way the intensity of the nth line is In = Imax2n The circular shape of the pole indicates
that the in-plane nanocrystal distribution is uniform This hypothesis is supported by the analysis of
the cut of the (200) pole image at χ=55 shown in figure 3c no difference in intensity is observable
varying angle confirming that any preferential in-plane direction does not exist
The (111) (200) and (220) LiF pole figures for the γ-irradiated LiF sample are shown in figure 4 For
this sample perfect (111) texture is presented (a) The FWHM of the (111) (200) and (220) LiF poles
are 5deg 8deg and 7deg respectively The detailed (111) pole in the range χlt30deg (b) and the cut of the (200)
pole figure at χ~55deg (c) are also reported The (111) LiF pole profile is perfectly circular and the (200)
pole -scan is constant indicating a high in-plane isotropy differently from what we observed for non-
irradiated LiF sample in which a low fraction of slightly misoriented nanocrystals can be inferred
(a)
(b) (c)
Figure 4 2d and 3d (111) (200) and (220) LiF pole figures of the γ-irradiated LiF
nanostructures (a) The perfect texture is shown Magnification of (111) LiF pole
figure χ lt30deg (b) and -scan of (200) figure demonstrating in-plane isotropy (c)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
5
It must be emphasized that the difference is very small an analysis of the (111) LiF pole figures
revealed that the integrated intensity of the range χlt10deg (Iχlt10) to the integrated intensity of the total
(111) pole figure (Itotal) ratio varies from 1495 (for the non-irradiated LiF sample) to 1505 (for the
sample γ-irradiated at RT with dose 83 kGy) Conversely the pole maximum is incresed of about 20
in the irradiated sample confirming the effect of the structure improving due to the γ-irradiation
In figure 5 the (111) (400) and (220) CaF2 pole images of non-irradiated CaF2 sample are reported (a)
Also in this case the presence of a good (111) texture is evident The FWHM of (111) (400) and
(220) poles are 5deg 7deg and 7deg The (111) peak profile is circular down to the lowest intensity and no
evidence of peak broadening was observed The pole is misaligned respect to the centre of about 05deg
as can be seen in figure 5b Since the measurement was repeated several times an error in the
mounting of the sample can be excluded A different profile of the -scan performed on the (400) and
(220) poles was recorded (figure 5c) characterised by a weak intensity dependence vs This
behaviour is due to the (111) CaF2 direction not exactly perpendicular to the substrate surface
(a)
(b) (c)
Figure 5 2d and 3d (111) (200) and (220) CaF2 pole figures of non-irradiated
CaF2 nanostructures (a) Magnification of (111) CaF2 pole figure χ lt30deg (b) A
misalignment of ~05deg is present and is consistent with the (400) (220) -scan (c)
Not reported here the poles for the γ-irradiated CaF2 sample revealed the development of more strong
(111) texture The FWHM of the (111) pole is about 4deg indicating a very small mosaic spread
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
6
32 Thin-film structures with nanocrystals of various fluoride materials
To establish the influence of content of LiF nanocrystals with given size on PL spectra of multilayers
two LiFCaF2 structures have been prepared The first LiFCaF2(1) (figure 1b period 1) is the 48-
period structure of 100 nm LiF-nanolayers and 50 nm CaF2-nanolayers The next LiFCaF2(2) is the
24-period structure consisting of 100 nm LiF- and 220 nm CaF2-nanolayers (figure 1b period 2)
(a) LiF (111) LiF (111) CaF2 (111)
Figure 6 3d (111) LiF CaF2 pole images of fresh LiFCaF2(1) (left) and LiFCaF2(2) multilayers
(middle right) (a) XRD patterns of LiFCaF2(2) before (1) after irradiation (2) and fresh LiFCaF2(1)
(3) (b) Transmission spectra of the multilayers and substrate (c) Reflection spectra of LiFCaF2(1) vs
angles of incidence in the range 20ordmndash50ordm (d) The graphs are p-polarized light
Both multilayers were composed of ~100 nm LiF and ~50 nm CaF2 nanocrystals and were c-oriented
structures (figures 6ab) In figure 6a the (111) LiF and CaF2 pole images of as-prepared LiFCaF2(1)
(left) and LiFCaF2(2) samples (middle right) are reported A well-resolved (111) LiF texture is
present on both cases The quantity of used isolines are 128 and the minimal and maximal intensities
in the (111) LiF pole figures are about 910 and 283 cps for the LiFCaF2(1) samples and 450 and
1154 cps for the LiFCaF2(2) samples This is due to the result LiF thickness in the LiFCaF2(1)
sample (45 μm) 27 time larger with respect to the LiFCaF2(2) sample (17 μm) The CaF2 pole image
(figure 6a right) indicates that the preferential nanocrystal orientation is (111) direction The
crystallinity and (111) texture improving for the γ-irradiated LiFCaF2 samples is supported by the
XRD patterns shown in figure 6b strong difference is observable between the data measured for
LiFCaF2(2) before (curve 1) and after γ-irradiation at RT with dose 83 kGy (curve 2)
High-reflectivity and transmissivity bands are provided by the LiFCaF2 structures (figure 2c) Spectral
positions of the bands were not changed after γ-irradiation but were sensitive to the polarization state
and angle of incidence of light see figure 2d The LiFCaF2 structures covered at the surface by CaF2
nanolayers are more mechanically stable and resistant to external influences than LiF nanostructures
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
7
33 Optical absorption features of non-irradiated thin-film structures
OA spectra of non-irradiated LiF nanostructures and initial crystals with small content of Mg2+
O2ndash
and OHndash ions [13] show well-resolved absorption of Mg
2+ colloids [11 12] (figure 7a) (The non-
irradiated and γ-irradiated substrates remain non-absorbing in the above spectral range) According to
the literature besides Mg colloids with the absorption band peaked at 44ndash46 eV the low-wavelength
absorption band at 36ndash41 eV related to the formation of more large Mg colloids or intrinsic Li
colloids [11 12] are reliably distinguished in non-irradiated LiF nanostructures (figure 7a) [21] and
initial crystals γ-irradiated with various doses and bleached by annealing after irradiation (figure 7a
insert) [13 14]
Figure 7 OA spectra of non-coloured (a) and PL spectra of γ-coloured nano (bold curve) and bulk
(solid curve) crystalline structures (b) and the structures with various LiF contents (c)
34 PL spectra of the irradiated thin-film structures
Non-presented here PL spectra of γ-irradiated CaF2 nanocrystals are composed of the reference 425
nm band excited at the wavelength of 370 nm The PL spectra of initial LiF crystal LiF and LiFCaF2
nanostructures having the same size of LiF nanocrystals and irradiated in analogous conditions are
given in figures 7bc In comparison with the initial crystals an increase of F3+-CCs excitation in the
region of Mg colloids absorption in nanostructures is observed together with an enhanced emission in
the green region with respect to the red one for γ-irradiated film structures (figures 7b) The
normalized emission spectra of nanostructures with various LiF content (bold) have the same shape
the F3+ photoluminescence band intensity at λmax = 538 nm increases of the same factor in comparison
with the F2 emission at 670 nm with respect to the spectrum of the crystal (solid curve) The PL
spectra show an increase (correlated with LiF nanocrystal content) of the intensities of F3+ and F2
bands (figure 7c) These results could be explained by the high structural and optical qualities of these
nanostructures (the overall emission is proportional to the quantity of luminescent LiF nanocrystals)
and by the nanocrystal purity with metal excess collection in their boundaries regions [22]
4 Thin-film structures with semiconductor and dielectric nanocrystals We measured nonlinear optical (NLO) effects for the reference films (figure 8a curve 1) elaborated
multilayers (figure 8a curves 2 3) and specially-elaborated multipeak TFIs containing c-oriented
cubic CdS nanocrystals of defined sizes as reported in figure 8 Sample 3 and TFIs intermediate layers
are composite film structures with semiconductor (CdS) and dielectric (CaF2) nanocrystals (figure 1c)
Separation of the transient shift and absorption saturation in TFIs gives us the features of both effects
Characteristic 1ndash2 ps decay of the shift confirms the metal clusters nature of the effect [23 24]
Maximal NLO effects in nanocrystals are increased with size reduction and are enhanced by extra
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
8
excitation power pulse durability [20 22] and γ-irradiation [19] These effects can be explained by
accumulation of colloids and electrons at nanocrystal boundaries
Figure 8 NLO characteristics detected for (a) reference films (1) multilayers (2 3) (b) multipeak
TFIs with c-oriented cubic CdS nanocrystals of defined sizes (c) Transmission spectra of the TFI
before (B) and at time of excitation (time delay between the excitation and registration is zero) (A)
Impurities and nonstoichiometric excess tend to be expelled from the small crystalline core as the
distance a defect or impurity must move to reach the surface of a nanocrystal is very small
Self-purification of the nanocrystals can be explained through technological arguments and is an
intrinsic property of defects in nanocrystals prepared by the methods of alternative deposition of
nanolayers with thicknesses 150ndash10 nm Post-growth thermal treatments ionising radiation
bombardment and light irradiation of the nanocrystals are the next tools for the nanocrystal
purification metal colloids formation and the nanocrystal properties modification
5 Conclusion
The c-axis highly oriented thin-film multilayer structures composed of dielectric (LiF CaF2) and
semiconductor (CdS) nanocrystals prepared by thermal evaporation show enhanced photo-response
which is related to high-quality nanocrystals but at the same time depends strongly on the defect
content especially as far as their 1ndash2 ps nonlinearities are concerned Critical factors are nanocrystal
purity as well as metal impurities and nonstoichiometric excess collection in their boundaries regions
The nanostructures (more high-quality than original bulk structures) can be part of efficient emitting
elements detectors and modulators of light as well as a novel type of dosimeters Such optically
stimulated luminescence dosimeters (integrable with SiO2OH fibres) provide capability for remote
monitoring radiation locations which are difficult to access and hazardous These devices are relatively
simple small in size cheap in production and have low power consumption Moreover they are also
suitable for space radiation dose exploration In addition they can be used in other radiation
measurements and have interesting perspectives in the case of periodical nanostructures composed of
the nanolayers of CdS and LiF nanocrystals with high-contrast indices of refraction (figure 1c)
Acknowledgments
The authors are indebted to O Bilan A Pace and V Gremenok for their help in irradiation and
microstructure testing of the samples Many thanks are due to M A Vincenti S Tikhomirov and O
Buganov for their assistance during PL and NLO experiments This work is supported by the
Belarusian National Program for Crystalline and Molecular Structures Research Project CMS-35 and
by the grants of the ENEA Fellowships Programme (Frascati Research Center Rome Italy)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
9
6 References
[1] Poole Ch and Owens F 2003 Introduction to Nanotechnology (New York John Wiley)
[2] Goncharova O 1994 Semiconductor microcrystallites in thin-film matrix fabrication methods
optical properties and application prospects New Materials for Thin Film Functional
Electronic-Technological Components ed V Labunov (Minsk Nauka i Tekhnika) chapter 6
pp 99ndash176
[3] Baldacchini G Cremona M dAuria G Martelli S Montereali R M Montecchi M Burattini E
Grilli A and Raco A 1996 Nucl Instr Meth B 116 447ndash51
[4] Montereali R M 2002 Point Defects in Thin Insulating films of Lithium Fluoride for Optical
Microsystems Ferroelectric and Dielectric Thin Films (Handbook of Thin Films Materials
vol 3) ed H S Nalwa (New York Academic Press) chapter 7 pp 399ndash431
[5] Kumar M et al 2005 J Phys D Appl Phys 38 637ndash41
[6] Goncharova O 2005 Microstructure and properties of periodic multilayer thin-film structures
with nanocrystals Advances in Spectroscopy for Lasers and Sensing Proc NATO Advanced
Study Institute (Erice Sicily Italy 6ndash21 June 2005) (NATO Science Series II
Mathematics Physics and Chemistry vol 231) ed B Di Bartolo and O Forte (Berlin
Springer) p 556
[7] Goncharova O Karpushko F V and Sinitsyn G V 1983 Technical Physics 28 1142ndash44
[8] Pulker H K 1979 Appl Optics 18 1969ndash77
[9] Wang Y H Lu J D Wang R W Mao Y L and Cheng Y G 2008 Vacuum 82 1220ndash23
[10] Bryukvina L I Ermolaeva E A Pidgurskii S N Suvorova L F and Khulugurov V M 2006 Phys
Sol State 48 68ndash72
[11] Schwartz K K Lyushina A F and Vitol A Ya 1969 Sov Phys Sol State 11 1885ndash90
[12] Lushchik A Lushchik Ch Schwartz K Vasilchenko E Papaleo R Sorokin M Volkov A E
Neumann R and Trautmann C 2007 Phys Rev B 76 054114
[13] Baldacchini G Goncharova O Kalinov V S Montereali R M Nichelatti E Vincenti A and
Voitovich A P 2007 Phys Status Solidi C 4 744ndash48
[14] Baldacchini G Goncharova O Kalinov V S Montereali R M Vincenti A and Voitovich A P
2007 Phys Status Solidi C 4 1134ndash38
[15] Goncharova O and Demin V 1993 Photosensitive resistive nonlinear optical thin-film
heterostructures RF Patent 2089656
[16] Goncharova O and Demin V 1994 Photosensitive resistive nonlinear optical composite films
RF Patent 2103846
[17] Goncharova O and Demin V 1994 Narrow-band thin-film FabryndashPerot interferometer RF
Patent 2078358
[18] Goncharova O 1998 Light-induced ultrafast bleaching in films of different arranging of
semiconductor nanocrystals materials Proc Int Conf on Coherent and Nonlinear Optics
(Moscow Russia 29 June ndash 3 July 1998) (Moscow Moscow State University Press) p 246
[19] Goncharova O Kalinov V and Voitovich A 2004 Radiat Meas 38 775ndash79
[20] Goncharova O 1996 Picosecond all-optical switching in thin-film FabryndashPerot interferometers
and cavityless devices Notes and Perspectives of Nonlinear Optics (Nonlinear Optics vol 3)
ed O Keller (London World Scientific) pp 636ndash42
[21] Goncharova O and Gremenok V 2007 Comparative study of electronic structure of thin film
nanocrystals prepared by low-temperature vacuum deposition Proc Int Conf CLEOEurope-
2007 (Munich Germany 17ndash22 June 2007) p 1-1
[22] Goncharova O Montereali R M and Baldacchini G 2008 Abstr Int Conf ICL-2008 Lyon
France 7ndash11 July 2008) p 160
[23] Goncharova O 1996 Studies on a Nature of the Picosecond Transient Absorption in Thin Films
Activated by Semiconductor or Metal Nanocrystals Proc Int Conf EQEC-1996 (Hamburg
Germany 8ndash13 Sept 1996) p 87
[24] Z Lu and K Zhu 2008 J Phys B At Mol Opt Phys 41 185503ndash09
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
10
3 Thin-film structures with dielectric nanocrystals
31 Thin-film structures with nanocrystals of one fluoride material
X-ray diffraction (XRD)- SEM- and AFM-results show that non-irradiated multilayers are structures
with definite size of nanocrystals (Final thickness of LiF CaF2 and LiFCaF2 structures is
approximately 65 μm) Presence of (111) and (222) peaks in XRD data of the multilayers indicates
that they have c-axis orientation perpendicular to the substrate surfaces The XRD patterns of LiF and
CaF2 multilayers see figure 2 show intense (111) peaks at 2θ = 387ordm 283ordm and a considerably less
intense (222) peaks at 2θ = 831ordm 585ordm respectively Not-presented here XRD- SEM- and AFM-
results validate the fact that irradiation neither causes a change in the packing nor increases the size of
nanocrystals The (111) peaks prevail in the XRD-patterns of samples and γ-irradiation with the dose
of 83 kGy only improves the crystallinity and the orientation of nanostructures (increase in the
intensities of (111) peaks) The XRD results correlate well with the texture analysis (figures 3ndash5)
(a)
(b) (c)
Figure 3 2d and 3d (111) (200) and (220) LiF pole figures of the non-irradiated LiF
nanostructures (a) Magnification of (111) LiF pole figure in the region χ lt30deg (b)
and -scan of the (200) LiF pole figure demonstrating the in-plane isotropy (c)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
4
In figure 3a two (2d) and three dimensional (3d) (111) (200) and (220) LiF pole figures of the non-
irradiated LiF sample are reported A sharp (111) texture is present The Full Width at Half Maximum
(FWHM) of the pole located at χ=0 in the (111) pole figure is about 6deg and the FWHMs of both (200)
and (220) poles are 8deg This is due to a very low mosaic spread in the growth direction Figure 3b
shows a magnification of the (111) pole figure in the range χ lt30deg The isointensity lines were chosen
in the following way the intensity of the nth line is In = Imax2n The circular shape of the pole indicates
that the in-plane nanocrystal distribution is uniform This hypothesis is supported by the analysis of
the cut of the (200) pole image at χ=55 shown in figure 3c no difference in intensity is observable
varying angle confirming that any preferential in-plane direction does not exist
The (111) (200) and (220) LiF pole figures for the γ-irradiated LiF sample are shown in figure 4 For
this sample perfect (111) texture is presented (a) The FWHM of the (111) (200) and (220) LiF poles
are 5deg 8deg and 7deg respectively The detailed (111) pole in the range χlt30deg (b) and the cut of the (200)
pole figure at χ~55deg (c) are also reported The (111) LiF pole profile is perfectly circular and the (200)
pole -scan is constant indicating a high in-plane isotropy differently from what we observed for non-
irradiated LiF sample in which a low fraction of slightly misoriented nanocrystals can be inferred
(a)
(b) (c)
Figure 4 2d and 3d (111) (200) and (220) LiF pole figures of the γ-irradiated LiF
nanostructures (a) The perfect texture is shown Magnification of (111) LiF pole
figure χ lt30deg (b) and -scan of (200) figure demonstrating in-plane isotropy (c)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
5
It must be emphasized that the difference is very small an analysis of the (111) LiF pole figures
revealed that the integrated intensity of the range χlt10deg (Iχlt10) to the integrated intensity of the total
(111) pole figure (Itotal) ratio varies from 1495 (for the non-irradiated LiF sample) to 1505 (for the
sample γ-irradiated at RT with dose 83 kGy) Conversely the pole maximum is incresed of about 20
in the irradiated sample confirming the effect of the structure improving due to the γ-irradiation
In figure 5 the (111) (400) and (220) CaF2 pole images of non-irradiated CaF2 sample are reported (a)
Also in this case the presence of a good (111) texture is evident The FWHM of (111) (400) and
(220) poles are 5deg 7deg and 7deg The (111) peak profile is circular down to the lowest intensity and no
evidence of peak broadening was observed The pole is misaligned respect to the centre of about 05deg
as can be seen in figure 5b Since the measurement was repeated several times an error in the
mounting of the sample can be excluded A different profile of the -scan performed on the (400) and
(220) poles was recorded (figure 5c) characterised by a weak intensity dependence vs This
behaviour is due to the (111) CaF2 direction not exactly perpendicular to the substrate surface
(a)
(b) (c)
Figure 5 2d and 3d (111) (200) and (220) CaF2 pole figures of non-irradiated
CaF2 nanostructures (a) Magnification of (111) CaF2 pole figure χ lt30deg (b) A
misalignment of ~05deg is present and is consistent with the (400) (220) -scan (c)
Not reported here the poles for the γ-irradiated CaF2 sample revealed the development of more strong
(111) texture The FWHM of the (111) pole is about 4deg indicating a very small mosaic spread
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
6
32 Thin-film structures with nanocrystals of various fluoride materials
To establish the influence of content of LiF nanocrystals with given size on PL spectra of multilayers
two LiFCaF2 structures have been prepared The first LiFCaF2(1) (figure 1b period 1) is the 48-
period structure of 100 nm LiF-nanolayers and 50 nm CaF2-nanolayers The next LiFCaF2(2) is the
24-period structure consisting of 100 nm LiF- and 220 nm CaF2-nanolayers (figure 1b period 2)
(a) LiF (111) LiF (111) CaF2 (111)
Figure 6 3d (111) LiF CaF2 pole images of fresh LiFCaF2(1) (left) and LiFCaF2(2) multilayers
(middle right) (a) XRD patterns of LiFCaF2(2) before (1) after irradiation (2) and fresh LiFCaF2(1)
(3) (b) Transmission spectra of the multilayers and substrate (c) Reflection spectra of LiFCaF2(1) vs
angles of incidence in the range 20ordmndash50ordm (d) The graphs are p-polarized light
Both multilayers were composed of ~100 nm LiF and ~50 nm CaF2 nanocrystals and were c-oriented
structures (figures 6ab) In figure 6a the (111) LiF and CaF2 pole images of as-prepared LiFCaF2(1)
(left) and LiFCaF2(2) samples (middle right) are reported A well-resolved (111) LiF texture is
present on both cases The quantity of used isolines are 128 and the minimal and maximal intensities
in the (111) LiF pole figures are about 910 and 283 cps for the LiFCaF2(1) samples and 450 and
1154 cps for the LiFCaF2(2) samples This is due to the result LiF thickness in the LiFCaF2(1)
sample (45 μm) 27 time larger with respect to the LiFCaF2(2) sample (17 μm) The CaF2 pole image
(figure 6a right) indicates that the preferential nanocrystal orientation is (111) direction The
crystallinity and (111) texture improving for the γ-irradiated LiFCaF2 samples is supported by the
XRD patterns shown in figure 6b strong difference is observable between the data measured for
LiFCaF2(2) before (curve 1) and after γ-irradiation at RT with dose 83 kGy (curve 2)
High-reflectivity and transmissivity bands are provided by the LiFCaF2 structures (figure 2c) Spectral
positions of the bands were not changed after γ-irradiation but were sensitive to the polarization state
and angle of incidence of light see figure 2d The LiFCaF2 structures covered at the surface by CaF2
nanolayers are more mechanically stable and resistant to external influences than LiF nanostructures
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
7
33 Optical absorption features of non-irradiated thin-film structures
OA spectra of non-irradiated LiF nanostructures and initial crystals with small content of Mg2+
O2ndash
and OHndash ions [13] show well-resolved absorption of Mg
2+ colloids [11 12] (figure 7a) (The non-
irradiated and γ-irradiated substrates remain non-absorbing in the above spectral range) According to
the literature besides Mg colloids with the absorption band peaked at 44ndash46 eV the low-wavelength
absorption band at 36ndash41 eV related to the formation of more large Mg colloids or intrinsic Li
colloids [11 12] are reliably distinguished in non-irradiated LiF nanostructures (figure 7a) [21] and
initial crystals γ-irradiated with various doses and bleached by annealing after irradiation (figure 7a
insert) [13 14]
Figure 7 OA spectra of non-coloured (a) and PL spectra of γ-coloured nano (bold curve) and bulk
(solid curve) crystalline structures (b) and the structures with various LiF contents (c)
34 PL spectra of the irradiated thin-film structures
Non-presented here PL spectra of γ-irradiated CaF2 nanocrystals are composed of the reference 425
nm band excited at the wavelength of 370 nm The PL spectra of initial LiF crystal LiF and LiFCaF2
nanostructures having the same size of LiF nanocrystals and irradiated in analogous conditions are
given in figures 7bc In comparison with the initial crystals an increase of F3+-CCs excitation in the
region of Mg colloids absorption in nanostructures is observed together with an enhanced emission in
the green region with respect to the red one for γ-irradiated film structures (figures 7b) The
normalized emission spectra of nanostructures with various LiF content (bold) have the same shape
the F3+ photoluminescence band intensity at λmax = 538 nm increases of the same factor in comparison
with the F2 emission at 670 nm with respect to the spectrum of the crystal (solid curve) The PL
spectra show an increase (correlated with LiF nanocrystal content) of the intensities of F3+ and F2
bands (figure 7c) These results could be explained by the high structural and optical qualities of these
nanostructures (the overall emission is proportional to the quantity of luminescent LiF nanocrystals)
and by the nanocrystal purity with metal excess collection in their boundaries regions [22]
4 Thin-film structures with semiconductor and dielectric nanocrystals We measured nonlinear optical (NLO) effects for the reference films (figure 8a curve 1) elaborated
multilayers (figure 8a curves 2 3) and specially-elaborated multipeak TFIs containing c-oriented
cubic CdS nanocrystals of defined sizes as reported in figure 8 Sample 3 and TFIs intermediate layers
are composite film structures with semiconductor (CdS) and dielectric (CaF2) nanocrystals (figure 1c)
Separation of the transient shift and absorption saturation in TFIs gives us the features of both effects
Characteristic 1ndash2 ps decay of the shift confirms the metal clusters nature of the effect [23 24]
Maximal NLO effects in nanocrystals are increased with size reduction and are enhanced by extra
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
8
excitation power pulse durability [20 22] and γ-irradiation [19] These effects can be explained by
accumulation of colloids and electrons at nanocrystal boundaries
Figure 8 NLO characteristics detected for (a) reference films (1) multilayers (2 3) (b) multipeak
TFIs with c-oriented cubic CdS nanocrystals of defined sizes (c) Transmission spectra of the TFI
before (B) and at time of excitation (time delay between the excitation and registration is zero) (A)
Impurities and nonstoichiometric excess tend to be expelled from the small crystalline core as the
distance a defect or impurity must move to reach the surface of a nanocrystal is very small
Self-purification of the nanocrystals can be explained through technological arguments and is an
intrinsic property of defects in nanocrystals prepared by the methods of alternative deposition of
nanolayers with thicknesses 150ndash10 nm Post-growth thermal treatments ionising radiation
bombardment and light irradiation of the nanocrystals are the next tools for the nanocrystal
purification metal colloids formation and the nanocrystal properties modification
5 Conclusion
The c-axis highly oriented thin-film multilayer structures composed of dielectric (LiF CaF2) and
semiconductor (CdS) nanocrystals prepared by thermal evaporation show enhanced photo-response
which is related to high-quality nanocrystals but at the same time depends strongly on the defect
content especially as far as their 1ndash2 ps nonlinearities are concerned Critical factors are nanocrystal
purity as well as metal impurities and nonstoichiometric excess collection in their boundaries regions
The nanostructures (more high-quality than original bulk structures) can be part of efficient emitting
elements detectors and modulators of light as well as a novel type of dosimeters Such optically
stimulated luminescence dosimeters (integrable with SiO2OH fibres) provide capability for remote
monitoring radiation locations which are difficult to access and hazardous These devices are relatively
simple small in size cheap in production and have low power consumption Moreover they are also
suitable for space radiation dose exploration In addition they can be used in other radiation
measurements and have interesting perspectives in the case of periodical nanostructures composed of
the nanolayers of CdS and LiF nanocrystals with high-contrast indices of refraction (figure 1c)
Acknowledgments
The authors are indebted to O Bilan A Pace and V Gremenok for their help in irradiation and
microstructure testing of the samples Many thanks are due to M A Vincenti S Tikhomirov and O
Buganov for their assistance during PL and NLO experiments This work is supported by the
Belarusian National Program for Crystalline and Molecular Structures Research Project CMS-35 and
by the grants of the ENEA Fellowships Programme (Frascati Research Center Rome Italy)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
9
6 References
[1] Poole Ch and Owens F 2003 Introduction to Nanotechnology (New York John Wiley)
[2] Goncharova O 1994 Semiconductor microcrystallites in thin-film matrix fabrication methods
optical properties and application prospects New Materials for Thin Film Functional
Electronic-Technological Components ed V Labunov (Minsk Nauka i Tekhnika) chapter 6
pp 99ndash176
[3] Baldacchini G Cremona M dAuria G Martelli S Montereali R M Montecchi M Burattini E
Grilli A and Raco A 1996 Nucl Instr Meth B 116 447ndash51
[4] Montereali R M 2002 Point Defects in Thin Insulating films of Lithium Fluoride for Optical
Microsystems Ferroelectric and Dielectric Thin Films (Handbook of Thin Films Materials
vol 3) ed H S Nalwa (New York Academic Press) chapter 7 pp 399ndash431
[5] Kumar M et al 2005 J Phys D Appl Phys 38 637ndash41
[6] Goncharova O 2005 Microstructure and properties of periodic multilayer thin-film structures
with nanocrystals Advances in Spectroscopy for Lasers and Sensing Proc NATO Advanced
Study Institute (Erice Sicily Italy 6ndash21 June 2005) (NATO Science Series II
Mathematics Physics and Chemistry vol 231) ed B Di Bartolo and O Forte (Berlin
Springer) p 556
[7] Goncharova O Karpushko F V and Sinitsyn G V 1983 Technical Physics 28 1142ndash44
[8] Pulker H K 1979 Appl Optics 18 1969ndash77
[9] Wang Y H Lu J D Wang R W Mao Y L and Cheng Y G 2008 Vacuum 82 1220ndash23
[10] Bryukvina L I Ermolaeva E A Pidgurskii S N Suvorova L F and Khulugurov V M 2006 Phys
Sol State 48 68ndash72
[11] Schwartz K K Lyushina A F and Vitol A Ya 1969 Sov Phys Sol State 11 1885ndash90
[12] Lushchik A Lushchik Ch Schwartz K Vasilchenko E Papaleo R Sorokin M Volkov A E
Neumann R and Trautmann C 2007 Phys Rev B 76 054114
[13] Baldacchini G Goncharova O Kalinov V S Montereali R M Nichelatti E Vincenti A and
Voitovich A P 2007 Phys Status Solidi C 4 744ndash48
[14] Baldacchini G Goncharova O Kalinov V S Montereali R M Vincenti A and Voitovich A P
2007 Phys Status Solidi C 4 1134ndash38
[15] Goncharova O and Demin V 1993 Photosensitive resistive nonlinear optical thin-film
heterostructures RF Patent 2089656
[16] Goncharova O and Demin V 1994 Photosensitive resistive nonlinear optical composite films
RF Patent 2103846
[17] Goncharova O and Demin V 1994 Narrow-band thin-film FabryndashPerot interferometer RF
Patent 2078358
[18] Goncharova O 1998 Light-induced ultrafast bleaching in films of different arranging of
semiconductor nanocrystals materials Proc Int Conf on Coherent and Nonlinear Optics
(Moscow Russia 29 June ndash 3 July 1998) (Moscow Moscow State University Press) p 246
[19] Goncharova O Kalinov V and Voitovich A 2004 Radiat Meas 38 775ndash79
[20] Goncharova O 1996 Picosecond all-optical switching in thin-film FabryndashPerot interferometers
and cavityless devices Notes and Perspectives of Nonlinear Optics (Nonlinear Optics vol 3)
ed O Keller (London World Scientific) pp 636ndash42
[21] Goncharova O and Gremenok V 2007 Comparative study of electronic structure of thin film
nanocrystals prepared by low-temperature vacuum deposition Proc Int Conf CLEOEurope-
2007 (Munich Germany 17ndash22 June 2007) p 1-1
[22] Goncharova O Montereali R M and Baldacchini G 2008 Abstr Int Conf ICL-2008 Lyon
France 7ndash11 July 2008) p 160
[23] Goncharova O 1996 Studies on a Nature of the Picosecond Transient Absorption in Thin Films
Activated by Semiconductor or Metal Nanocrystals Proc Int Conf EQEC-1996 (Hamburg
Germany 8ndash13 Sept 1996) p 87
[24] Z Lu and K Zhu 2008 J Phys B At Mol Opt Phys 41 185503ndash09
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
10
In figure 3a two (2d) and three dimensional (3d) (111) (200) and (220) LiF pole figures of the non-
irradiated LiF sample are reported A sharp (111) texture is present The Full Width at Half Maximum
(FWHM) of the pole located at χ=0 in the (111) pole figure is about 6deg and the FWHMs of both (200)
and (220) poles are 8deg This is due to a very low mosaic spread in the growth direction Figure 3b
shows a magnification of the (111) pole figure in the range χ lt30deg The isointensity lines were chosen
in the following way the intensity of the nth line is In = Imax2n The circular shape of the pole indicates
that the in-plane nanocrystal distribution is uniform This hypothesis is supported by the analysis of
the cut of the (200) pole image at χ=55 shown in figure 3c no difference in intensity is observable
varying angle confirming that any preferential in-plane direction does not exist
The (111) (200) and (220) LiF pole figures for the γ-irradiated LiF sample are shown in figure 4 For
this sample perfect (111) texture is presented (a) The FWHM of the (111) (200) and (220) LiF poles
are 5deg 8deg and 7deg respectively The detailed (111) pole in the range χlt30deg (b) and the cut of the (200)
pole figure at χ~55deg (c) are also reported The (111) LiF pole profile is perfectly circular and the (200)
pole -scan is constant indicating a high in-plane isotropy differently from what we observed for non-
irradiated LiF sample in which a low fraction of slightly misoriented nanocrystals can be inferred
(a)
(b) (c)
Figure 4 2d and 3d (111) (200) and (220) LiF pole figures of the γ-irradiated LiF
nanostructures (a) The perfect texture is shown Magnification of (111) LiF pole
figure χ lt30deg (b) and -scan of (200) figure demonstrating in-plane isotropy (c)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
5
It must be emphasized that the difference is very small an analysis of the (111) LiF pole figures
revealed that the integrated intensity of the range χlt10deg (Iχlt10) to the integrated intensity of the total
(111) pole figure (Itotal) ratio varies from 1495 (for the non-irradiated LiF sample) to 1505 (for the
sample γ-irradiated at RT with dose 83 kGy) Conversely the pole maximum is incresed of about 20
in the irradiated sample confirming the effect of the structure improving due to the γ-irradiation
In figure 5 the (111) (400) and (220) CaF2 pole images of non-irradiated CaF2 sample are reported (a)
Also in this case the presence of a good (111) texture is evident The FWHM of (111) (400) and
(220) poles are 5deg 7deg and 7deg The (111) peak profile is circular down to the lowest intensity and no
evidence of peak broadening was observed The pole is misaligned respect to the centre of about 05deg
as can be seen in figure 5b Since the measurement was repeated several times an error in the
mounting of the sample can be excluded A different profile of the -scan performed on the (400) and
(220) poles was recorded (figure 5c) characterised by a weak intensity dependence vs This
behaviour is due to the (111) CaF2 direction not exactly perpendicular to the substrate surface
(a)
(b) (c)
Figure 5 2d and 3d (111) (200) and (220) CaF2 pole figures of non-irradiated
CaF2 nanostructures (a) Magnification of (111) CaF2 pole figure χ lt30deg (b) A
misalignment of ~05deg is present and is consistent with the (400) (220) -scan (c)
Not reported here the poles for the γ-irradiated CaF2 sample revealed the development of more strong
(111) texture The FWHM of the (111) pole is about 4deg indicating a very small mosaic spread
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
6
32 Thin-film structures with nanocrystals of various fluoride materials
To establish the influence of content of LiF nanocrystals with given size on PL spectra of multilayers
two LiFCaF2 structures have been prepared The first LiFCaF2(1) (figure 1b period 1) is the 48-
period structure of 100 nm LiF-nanolayers and 50 nm CaF2-nanolayers The next LiFCaF2(2) is the
24-period structure consisting of 100 nm LiF- and 220 nm CaF2-nanolayers (figure 1b period 2)
(a) LiF (111) LiF (111) CaF2 (111)
Figure 6 3d (111) LiF CaF2 pole images of fresh LiFCaF2(1) (left) and LiFCaF2(2) multilayers
(middle right) (a) XRD patterns of LiFCaF2(2) before (1) after irradiation (2) and fresh LiFCaF2(1)
(3) (b) Transmission spectra of the multilayers and substrate (c) Reflection spectra of LiFCaF2(1) vs
angles of incidence in the range 20ordmndash50ordm (d) The graphs are p-polarized light
Both multilayers were composed of ~100 nm LiF and ~50 nm CaF2 nanocrystals and were c-oriented
structures (figures 6ab) In figure 6a the (111) LiF and CaF2 pole images of as-prepared LiFCaF2(1)
(left) and LiFCaF2(2) samples (middle right) are reported A well-resolved (111) LiF texture is
present on both cases The quantity of used isolines are 128 and the minimal and maximal intensities
in the (111) LiF pole figures are about 910 and 283 cps for the LiFCaF2(1) samples and 450 and
1154 cps for the LiFCaF2(2) samples This is due to the result LiF thickness in the LiFCaF2(1)
sample (45 μm) 27 time larger with respect to the LiFCaF2(2) sample (17 μm) The CaF2 pole image
(figure 6a right) indicates that the preferential nanocrystal orientation is (111) direction The
crystallinity and (111) texture improving for the γ-irradiated LiFCaF2 samples is supported by the
XRD patterns shown in figure 6b strong difference is observable between the data measured for
LiFCaF2(2) before (curve 1) and after γ-irradiation at RT with dose 83 kGy (curve 2)
High-reflectivity and transmissivity bands are provided by the LiFCaF2 structures (figure 2c) Spectral
positions of the bands were not changed after γ-irradiation but were sensitive to the polarization state
and angle of incidence of light see figure 2d The LiFCaF2 structures covered at the surface by CaF2
nanolayers are more mechanically stable and resistant to external influences than LiF nanostructures
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
7
33 Optical absorption features of non-irradiated thin-film structures
OA spectra of non-irradiated LiF nanostructures and initial crystals with small content of Mg2+
O2ndash
and OHndash ions [13] show well-resolved absorption of Mg
2+ colloids [11 12] (figure 7a) (The non-
irradiated and γ-irradiated substrates remain non-absorbing in the above spectral range) According to
the literature besides Mg colloids with the absorption band peaked at 44ndash46 eV the low-wavelength
absorption band at 36ndash41 eV related to the formation of more large Mg colloids or intrinsic Li
colloids [11 12] are reliably distinguished in non-irradiated LiF nanostructures (figure 7a) [21] and
initial crystals γ-irradiated with various doses and bleached by annealing after irradiation (figure 7a
insert) [13 14]
Figure 7 OA spectra of non-coloured (a) and PL spectra of γ-coloured nano (bold curve) and bulk
(solid curve) crystalline structures (b) and the structures with various LiF contents (c)
34 PL spectra of the irradiated thin-film structures
Non-presented here PL spectra of γ-irradiated CaF2 nanocrystals are composed of the reference 425
nm band excited at the wavelength of 370 nm The PL spectra of initial LiF crystal LiF and LiFCaF2
nanostructures having the same size of LiF nanocrystals and irradiated in analogous conditions are
given in figures 7bc In comparison with the initial crystals an increase of F3+-CCs excitation in the
region of Mg colloids absorption in nanostructures is observed together with an enhanced emission in
the green region with respect to the red one for γ-irradiated film structures (figures 7b) The
normalized emission spectra of nanostructures with various LiF content (bold) have the same shape
the F3+ photoluminescence band intensity at λmax = 538 nm increases of the same factor in comparison
with the F2 emission at 670 nm with respect to the spectrum of the crystal (solid curve) The PL
spectra show an increase (correlated with LiF nanocrystal content) of the intensities of F3+ and F2
bands (figure 7c) These results could be explained by the high structural and optical qualities of these
nanostructures (the overall emission is proportional to the quantity of luminescent LiF nanocrystals)
and by the nanocrystal purity with metal excess collection in their boundaries regions [22]
4 Thin-film structures with semiconductor and dielectric nanocrystals We measured nonlinear optical (NLO) effects for the reference films (figure 8a curve 1) elaborated
multilayers (figure 8a curves 2 3) and specially-elaborated multipeak TFIs containing c-oriented
cubic CdS nanocrystals of defined sizes as reported in figure 8 Sample 3 and TFIs intermediate layers
are composite film structures with semiconductor (CdS) and dielectric (CaF2) nanocrystals (figure 1c)
Separation of the transient shift and absorption saturation in TFIs gives us the features of both effects
Characteristic 1ndash2 ps decay of the shift confirms the metal clusters nature of the effect [23 24]
Maximal NLO effects in nanocrystals are increased with size reduction and are enhanced by extra
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
8
excitation power pulse durability [20 22] and γ-irradiation [19] These effects can be explained by
accumulation of colloids and electrons at nanocrystal boundaries
Figure 8 NLO characteristics detected for (a) reference films (1) multilayers (2 3) (b) multipeak
TFIs with c-oriented cubic CdS nanocrystals of defined sizes (c) Transmission spectra of the TFI
before (B) and at time of excitation (time delay between the excitation and registration is zero) (A)
Impurities and nonstoichiometric excess tend to be expelled from the small crystalline core as the
distance a defect or impurity must move to reach the surface of a nanocrystal is very small
Self-purification of the nanocrystals can be explained through technological arguments and is an
intrinsic property of defects in nanocrystals prepared by the methods of alternative deposition of
nanolayers with thicknesses 150ndash10 nm Post-growth thermal treatments ionising radiation
bombardment and light irradiation of the nanocrystals are the next tools for the nanocrystal
purification metal colloids formation and the nanocrystal properties modification
5 Conclusion
The c-axis highly oriented thin-film multilayer structures composed of dielectric (LiF CaF2) and
semiconductor (CdS) nanocrystals prepared by thermal evaporation show enhanced photo-response
which is related to high-quality nanocrystals but at the same time depends strongly on the defect
content especially as far as their 1ndash2 ps nonlinearities are concerned Critical factors are nanocrystal
purity as well as metal impurities and nonstoichiometric excess collection in their boundaries regions
The nanostructures (more high-quality than original bulk structures) can be part of efficient emitting
elements detectors and modulators of light as well as a novel type of dosimeters Such optically
stimulated luminescence dosimeters (integrable with SiO2OH fibres) provide capability for remote
monitoring radiation locations which are difficult to access and hazardous These devices are relatively
simple small in size cheap in production and have low power consumption Moreover they are also
suitable for space radiation dose exploration In addition they can be used in other radiation
measurements and have interesting perspectives in the case of periodical nanostructures composed of
the nanolayers of CdS and LiF nanocrystals with high-contrast indices of refraction (figure 1c)
Acknowledgments
The authors are indebted to O Bilan A Pace and V Gremenok for their help in irradiation and
microstructure testing of the samples Many thanks are due to M A Vincenti S Tikhomirov and O
Buganov for their assistance during PL and NLO experiments This work is supported by the
Belarusian National Program for Crystalline and Molecular Structures Research Project CMS-35 and
by the grants of the ENEA Fellowships Programme (Frascati Research Center Rome Italy)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
9
6 References
[1] Poole Ch and Owens F 2003 Introduction to Nanotechnology (New York John Wiley)
[2] Goncharova O 1994 Semiconductor microcrystallites in thin-film matrix fabrication methods
optical properties and application prospects New Materials for Thin Film Functional
Electronic-Technological Components ed V Labunov (Minsk Nauka i Tekhnika) chapter 6
pp 99ndash176
[3] Baldacchini G Cremona M dAuria G Martelli S Montereali R M Montecchi M Burattini E
Grilli A and Raco A 1996 Nucl Instr Meth B 116 447ndash51
[4] Montereali R M 2002 Point Defects in Thin Insulating films of Lithium Fluoride for Optical
Microsystems Ferroelectric and Dielectric Thin Films (Handbook of Thin Films Materials
vol 3) ed H S Nalwa (New York Academic Press) chapter 7 pp 399ndash431
[5] Kumar M et al 2005 J Phys D Appl Phys 38 637ndash41
[6] Goncharova O 2005 Microstructure and properties of periodic multilayer thin-film structures
with nanocrystals Advances in Spectroscopy for Lasers and Sensing Proc NATO Advanced
Study Institute (Erice Sicily Italy 6ndash21 June 2005) (NATO Science Series II
Mathematics Physics and Chemistry vol 231) ed B Di Bartolo and O Forte (Berlin
Springer) p 556
[7] Goncharova O Karpushko F V and Sinitsyn G V 1983 Technical Physics 28 1142ndash44
[8] Pulker H K 1979 Appl Optics 18 1969ndash77
[9] Wang Y H Lu J D Wang R W Mao Y L and Cheng Y G 2008 Vacuum 82 1220ndash23
[10] Bryukvina L I Ermolaeva E A Pidgurskii S N Suvorova L F and Khulugurov V M 2006 Phys
Sol State 48 68ndash72
[11] Schwartz K K Lyushina A F and Vitol A Ya 1969 Sov Phys Sol State 11 1885ndash90
[12] Lushchik A Lushchik Ch Schwartz K Vasilchenko E Papaleo R Sorokin M Volkov A E
Neumann R and Trautmann C 2007 Phys Rev B 76 054114
[13] Baldacchini G Goncharova O Kalinov V S Montereali R M Nichelatti E Vincenti A and
Voitovich A P 2007 Phys Status Solidi C 4 744ndash48
[14] Baldacchini G Goncharova O Kalinov V S Montereali R M Vincenti A and Voitovich A P
2007 Phys Status Solidi C 4 1134ndash38
[15] Goncharova O and Demin V 1993 Photosensitive resistive nonlinear optical thin-film
heterostructures RF Patent 2089656
[16] Goncharova O and Demin V 1994 Photosensitive resistive nonlinear optical composite films
RF Patent 2103846
[17] Goncharova O and Demin V 1994 Narrow-band thin-film FabryndashPerot interferometer RF
Patent 2078358
[18] Goncharova O 1998 Light-induced ultrafast bleaching in films of different arranging of
semiconductor nanocrystals materials Proc Int Conf on Coherent and Nonlinear Optics
(Moscow Russia 29 June ndash 3 July 1998) (Moscow Moscow State University Press) p 246
[19] Goncharova O Kalinov V and Voitovich A 2004 Radiat Meas 38 775ndash79
[20] Goncharova O 1996 Picosecond all-optical switching in thin-film FabryndashPerot interferometers
and cavityless devices Notes and Perspectives of Nonlinear Optics (Nonlinear Optics vol 3)
ed O Keller (London World Scientific) pp 636ndash42
[21] Goncharova O and Gremenok V 2007 Comparative study of electronic structure of thin film
nanocrystals prepared by low-temperature vacuum deposition Proc Int Conf CLEOEurope-
2007 (Munich Germany 17ndash22 June 2007) p 1-1
[22] Goncharova O Montereali R M and Baldacchini G 2008 Abstr Int Conf ICL-2008 Lyon
France 7ndash11 July 2008) p 160
[23] Goncharova O 1996 Studies on a Nature of the Picosecond Transient Absorption in Thin Films
Activated by Semiconductor or Metal Nanocrystals Proc Int Conf EQEC-1996 (Hamburg
Germany 8ndash13 Sept 1996) p 87
[24] Z Lu and K Zhu 2008 J Phys B At Mol Opt Phys 41 185503ndash09
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
10
It must be emphasized that the difference is very small an analysis of the (111) LiF pole figures
revealed that the integrated intensity of the range χlt10deg (Iχlt10) to the integrated intensity of the total
(111) pole figure (Itotal) ratio varies from 1495 (for the non-irradiated LiF sample) to 1505 (for the
sample γ-irradiated at RT with dose 83 kGy) Conversely the pole maximum is incresed of about 20
in the irradiated sample confirming the effect of the structure improving due to the γ-irradiation
In figure 5 the (111) (400) and (220) CaF2 pole images of non-irradiated CaF2 sample are reported (a)
Also in this case the presence of a good (111) texture is evident The FWHM of (111) (400) and
(220) poles are 5deg 7deg and 7deg The (111) peak profile is circular down to the lowest intensity and no
evidence of peak broadening was observed The pole is misaligned respect to the centre of about 05deg
as can be seen in figure 5b Since the measurement was repeated several times an error in the
mounting of the sample can be excluded A different profile of the -scan performed on the (400) and
(220) poles was recorded (figure 5c) characterised by a weak intensity dependence vs This
behaviour is due to the (111) CaF2 direction not exactly perpendicular to the substrate surface
(a)
(b) (c)
Figure 5 2d and 3d (111) (200) and (220) CaF2 pole figures of non-irradiated
CaF2 nanostructures (a) Magnification of (111) CaF2 pole figure χ lt30deg (b) A
misalignment of ~05deg is present and is consistent with the (400) (220) -scan (c)
Not reported here the poles for the γ-irradiated CaF2 sample revealed the development of more strong
(111) texture The FWHM of the (111) pole is about 4deg indicating a very small mosaic spread
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
6
32 Thin-film structures with nanocrystals of various fluoride materials
To establish the influence of content of LiF nanocrystals with given size on PL spectra of multilayers
two LiFCaF2 structures have been prepared The first LiFCaF2(1) (figure 1b period 1) is the 48-
period structure of 100 nm LiF-nanolayers and 50 nm CaF2-nanolayers The next LiFCaF2(2) is the
24-period structure consisting of 100 nm LiF- and 220 nm CaF2-nanolayers (figure 1b period 2)
(a) LiF (111) LiF (111) CaF2 (111)
Figure 6 3d (111) LiF CaF2 pole images of fresh LiFCaF2(1) (left) and LiFCaF2(2) multilayers
(middle right) (a) XRD patterns of LiFCaF2(2) before (1) after irradiation (2) and fresh LiFCaF2(1)
(3) (b) Transmission spectra of the multilayers and substrate (c) Reflection spectra of LiFCaF2(1) vs
angles of incidence in the range 20ordmndash50ordm (d) The graphs are p-polarized light
Both multilayers were composed of ~100 nm LiF and ~50 nm CaF2 nanocrystals and were c-oriented
structures (figures 6ab) In figure 6a the (111) LiF and CaF2 pole images of as-prepared LiFCaF2(1)
(left) and LiFCaF2(2) samples (middle right) are reported A well-resolved (111) LiF texture is
present on both cases The quantity of used isolines are 128 and the minimal and maximal intensities
in the (111) LiF pole figures are about 910 and 283 cps for the LiFCaF2(1) samples and 450 and
1154 cps for the LiFCaF2(2) samples This is due to the result LiF thickness in the LiFCaF2(1)
sample (45 μm) 27 time larger with respect to the LiFCaF2(2) sample (17 μm) The CaF2 pole image
(figure 6a right) indicates that the preferential nanocrystal orientation is (111) direction The
crystallinity and (111) texture improving for the γ-irradiated LiFCaF2 samples is supported by the
XRD patterns shown in figure 6b strong difference is observable between the data measured for
LiFCaF2(2) before (curve 1) and after γ-irradiation at RT with dose 83 kGy (curve 2)
High-reflectivity and transmissivity bands are provided by the LiFCaF2 structures (figure 2c) Spectral
positions of the bands were not changed after γ-irradiation but were sensitive to the polarization state
and angle of incidence of light see figure 2d The LiFCaF2 structures covered at the surface by CaF2
nanolayers are more mechanically stable and resistant to external influences than LiF nanostructures
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
7
33 Optical absorption features of non-irradiated thin-film structures
OA spectra of non-irradiated LiF nanostructures and initial crystals with small content of Mg2+
O2ndash
and OHndash ions [13] show well-resolved absorption of Mg
2+ colloids [11 12] (figure 7a) (The non-
irradiated and γ-irradiated substrates remain non-absorbing in the above spectral range) According to
the literature besides Mg colloids with the absorption band peaked at 44ndash46 eV the low-wavelength
absorption band at 36ndash41 eV related to the formation of more large Mg colloids or intrinsic Li
colloids [11 12] are reliably distinguished in non-irradiated LiF nanostructures (figure 7a) [21] and
initial crystals γ-irradiated with various doses and bleached by annealing after irradiation (figure 7a
insert) [13 14]
Figure 7 OA spectra of non-coloured (a) and PL spectra of γ-coloured nano (bold curve) and bulk
(solid curve) crystalline structures (b) and the structures with various LiF contents (c)
34 PL spectra of the irradiated thin-film structures
Non-presented here PL spectra of γ-irradiated CaF2 nanocrystals are composed of the reference 425
nm band excited at the wavelength of 370 nm The PL spectra of initial LiF crystal LiF and LiFCaF2
nanostructures having the same size of LiF nanocrystals and irradiated in analogous conditions are
given in figures 7bc In comparison with the initial crystals an increase of F3+-CCs excitation in the
region of Mg colloids absorption in nanostructures is observed together with an enhanced emission in
the green region with respect to the red one for γ-irradiated film structures (figures 7b) The
normalized emission spectra of nanostructures with various LiF content (bold) have the same shape
the F3+ photoluminescence band intensity at λmax = 538 nm increases of the same factor in comparison
with the F2 emission at 670 nm with respect to the spectrum of the crystal (solid curve) The PL
spectra show an increase (correlated with LiF nanocrystal content) of the intensities of F3+ and F2
bands (figure 7c) These results could be explained by the high structural and optical qualities of these
nanostructures (the overall emission is proportional to the quantity of luminescent LiF nanocrystals)
and by the nanocrystal purity with metal excess collection in their boundaries regions [22]
4 Thin-film structures with semiconductor and dielectric nanocrystals We measured nonlinear optical (NLO) effects for the reference films (figure 8a curve 1) elaborated
multilayers (figure 8a curves 2 3) and specially-elaborated multipeak TFIs containing c-oriented
cubic CdS nanocrystals of defined sizes as reported in figure 8 Sample 3 and TFIs intermediate layers
are composite film structures with semiconductor (CdS) and dielectric (CaF2) nanocrystals (figure 1c)
Separation of the transient shift and absorption saturation in TFIs gives us the features of both effects
Characteristic 1ndash2 ps decay of the shift confirms the metal clusters nature of the effect [23 24]
Maximal NLO effects in nanocrystals are increased with size reduction and are enhanced by extra
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
8
excitation power pulse durability [20 22] and γ-irradiation [19] These effects can be explained by
accumulation of colloids and electrons at nanocrystal boundaries
Figure 8 NLO characteristics detected for (a) reference films (1) multilayers (2 3) (b) multipeak
TFIs with c-oriented cubic CdS nanocrystals of defined sizes (c) Transmission spectra of the TFI
before (B) and at time of excitation (time delay between the excitation and registration is zero) (A)
Impurities and nonstoichiometric excess tend to be expelled from the small crystalline core as the
distance a defect or impurity must move to reach the surface of a nanocrystal is very small
Self-purification of the nanocrystals can be explained through technological arguments and is an
intrinsic property of defects in nanocrystals prepared by the methods of alternative deposition of
nanolayers with thicknesses 150ndash10 nm Post-growth thermal treatments ionising radiation
bombardment and light irradiation of the nanocrystals are the next tools for the nanocrystal
purification metal colloids formation and the nanocrystal properties modification
5 Conclusion
The c-axis highly oriented thin-film multilayer structures composed of dielectric (LiF CaF2) and
semiconductor (CdS) nanocrystals prepared by thermal evaporation show enhanced photo-response
which is related to high-quality nanocrystals but at the same time depends strongly on the defect
content especially as far as their 1ndash2 ps nonlinearities are concerned Critical factors are nanocrystal
purity as well as metal impurities and nonstoichiometric excess collection in their boundaries regions
The nanostructures (more high-quality than original bulk structures) can be part of efficient emitting
elements detectors and modulators of light as well as a novel type of dosimeters Such optically
stimulated luminescence dosimeters (integrable with SiO2OH fibres) provide capability for remote
monitoring radiation locations which are difficult to access and hazardous These devices are relatively
simple small in size cheap in production and have low power consumption Moreover they are also
suitable for space radiation dose exploration In addition they can be used in other radiation
measurements and have interesting perspectives in the case of periodical nanostructures composed of
the nanolayers of CdS and LiF nanocrystals with high-contrast indices of refraction (figure 1c)
Acknowledgments
The authors are indebted to O Bilan A Pace and V Gremenok for their help in irradiation and
microstructure testing of the samples Many thanks are due to M A Vincenti S Tikhomirov and O
Buganov for their assistance during PL and NLO experiments This work is supported by the
Belarusian National Program for Crystalline and Molecular Structures Research Project CMS-35 and
by the grants of the ENEA Fellowships Programme (Frascati Research Center Rome Italy)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
9
6 References
[1] Poole Ch and Owens F 2003 Introduction to Nanotechnology (New York John Wiley)
[2] Goncharova O 1994 Semiconductor microcrystallites in thin-film matrix fabrication methods
optical properties and application prospects New Materials for Thin Film Functional
Electronic-Technological Components ed V Labunov (Minsk Nauka i Tekhnika) chapter 6
pp 99ndash176
[3] Baldacchini G Cremona M dAuria G Martelli S Montereali R M Montecchi M Burattini E
Grilli A and Raco A 1996 Nucl Instr Meth B 116 447ndash51
[4] Montereali R M 2002 Point Defects in Thin Insulating films of Lithium Fluoride for Optical
Microsystems Ferroelectric and Dielectric Thin Films (Handbook of Thin Films Materials
vol 3) ed H S Nalwa (New York Academic Press) chapter 7 pp 399ndash431
[5] Kumar M et al 2005 J Phys D Appl Phys 38 637ndash41
[6] Goncharova O 2005 Microstructure and properties of periodic multilayer thin-film structures
with nanocrystals Advances in Spectroscopy for Lasers and Sensing Proc NATO Advanced
Study Institute (Erice Sicily Italy 6ndash21 June 2005) (NATO Science Series II
Mathematics Physics and Chemistry vol 231) ed B Di Bartolo and O Forte (Berlin
Springer) p 556
[7] Goncharova O Karpushko F V and Sinitsyn G V 1983 Technical Physics 28 1142ndash44
[8] Pulker H K 1979 Appl Optics 18 1969ndash77
[9] Wang Y H Lu J D Wang R W Mao Y L and Cheng Y G 2008 Vacuum 82 1220ndash23
[10] Bryukvina L I Ermolaeva E A Pidgurskii S N Suvorova L F and Khulugurov V M 2006 Phys
Sol State 48 68ndash72
[11] Schwartz K K Lyushina A F and Vitol A Ya 1969 Sov Phys Sol State 11 1885ndash90
[12] Lushchik A Lushchik Ch Schwartz K Vasilchenko E Papaleo R Sorokin M Volkov A E
Neumann R and Trautmann C 2007 Phys Rev B 76 054114
[13] Baldacchini G Goncharova O Kalinov V S Montereali R M Nichelatti E Vincenti A and
Voitovich A P 2007 Phys Status Solidi C 4 744ndash48
[14] Baldacchini G Goncharova O Kalinov V S Montereali R M Vincenti A and Voitovich A P
2007 Phys Status Solidi C 4 1134ndash38
[15] Goncharova O and Demin V 1993 Photosensitive resistive nonlinear optical thin-film
heterostructures RF Patent 2089656
[16] Goncharova O and Demin V 1994 Photosensitive resistive nonlinear optical composite films
RF Patent 2103846
[17] Goncharova O and Demin V 1994 Narrow-band thin-film FabryndashPerot interferometer RF
Patent 2078358
[18] Goncharova O 1998 Light-induced ultrafast bleaching in films of different arranging of
semiconductor nanocrystals materials Proc Int Conf on Coherent and Nonlinear Optics
(Moscow Russia 29 June ndash 3 July 1998) (Moscow Moscow State University Press) p 246
[19] Goncharova O Kalinov V and Voitovich A 2004 Radiat Meas 38 775ndash79
[20] Goncharova O 1996 Picosecond all-optical switching in thin-film FabryndashPerot interferometers
and cavityless devices Notes and Perspectives of Nonlinear Optics (Nonlinear Optics vol 3)
ed O Keller (London World Scientific) pp 636ndash42
[21] Goncharova O and Gremenok V 2007 Comparative study of electronic structure of thin film
nanocrystals prepared by low-temperature vacuum deposition Proc Int Conf CLEOEurope-
2007 (Munich Germany 17ndash22 June 2007) p 1-1
[22] Goncharova O Montereali R M and Baldacchini G 2008 Abstr Int Conf ICL-2008 Lyon
France 7ndash11 July 2008) p 160
[23] Goncharova O 1996 Studies on a Nature of the Picosecond Transient Absorption in Thin Films
Activated by Semiconductor or Metal Nanocrystals Proc Int Conf EQEC-1996 (Hamburg
Germany 8ndash13 Sept 1996) p 87
[24] Z Lu and K Zhu 2008 J Phys B At Mol Opt Phys 41 185503ndash09
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
10
32 Thin-film structures with nanocrystals of various fluoride materials
To establish the influence of content of LiF nanocrystals with given size on PL spectra of multilayers
two LiFCaF2 structures have been prepared The first LiFCaF2(1) (figure 1b period 1) is the 48-
period structure of 100 nm LiF-nanolayers and 50 nm CaF2-nanolayers The next LiFCaF2(2) is the
24-period structure consisting of 100 nm LiF- and 220 nm CaF2-nanolayers (figure 1b period 2)
(a) LiF (111) LiF (111) CaF2 (111)
Figure 6 3d (111) LiF CaF2 pole images of fresh LiFCaF2(1) (left) and LiFCaF2(2) multilayers
(middle right) (a) XRD patterns of LiFCaF2(2) before (1) after irradiation (2) and fresh LiFCaF2(1)
(3) (b) Transmission spectra of the multilayers and substrate (c) Reflection spectra of LiFCaF2(1) vs
angles of incidence in the range 20ordmndash50ordm (d) The graphs are p-polarized light
Both multilayers were composed of ~100 nm LiF and ~50 nm CaF2 nanocrystals and were c-oriented
structures (figures 6ab) In figure 6a the (111) LiF and CaF2 pole images of as-prepared LiFCaF2(1)
(left) and LiFCaF2(2) samples (middle right) are reported A well-resolved (111) LiF texture is
present on both cases The quantity of used isolines are 128 and the minimal and maximal intensities
in the (111) LiF pole figures are about 910 and 283 cps for the LiFCaF2(1) samples and 450 and
1154 cps for the LiFCaF2(2) samples This is due to the result LiF thickness in the LiFCaF2(1)
sample (45 μm) 27 time larger with respect to the LiFCaF2(2) sample (17 μm) The CaF2 pole image
(figure 6a right) indicates that the preferential nanocrystal orientation is (111) direction The
crystallinity and (111) texture improving for the γ-irradiated LiFCaF2 samples is supported by the
XRD patterns shown in figure 6b strong difference is observable between the data measured for
LiFCaF2(2) before (curve 1) and after γ-irradiation at RT with dose 83 kGy (curve 2)
High-reflectivity and transmissivity bands are provided by the LiFCaF2 structures (figure 2c) Spectral
positions of the bands were not changed after γ-irradiation but were sensitive to the polarization state
and angle of incidence of light see figure 2d The LiFCaF2 structures covered at the surface by CaF2
nanolayers are more mechanically stable and resistant to external influences than LiF nanostructures
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
7
33 Optical absorption features of non-irradiated thin-film structures
OA spectra of non-irradiated LiF nanostructures and initial crystals with small content of Mg2+
O2ndash
and OHndash ions [13] show well-resolved absorption of Mg
2+ colloids [11 12] (figure 7a) (The non-
irradiated and γ-irradiated substrates remain non-absorbing in the above spectral range) According to
the literature besides Mg colloids with the absorption band peaked at 44ndash46 eV the low-wavelength
absorption band at 36ndash41 eV related to the formation of more large Mg colloids or intrinsic Li
colloids [11 12] are reliably distinguished in non-irradiated LiF nanostructures (figure 7a) [21] and
initial crystals γ-irradiated with various doses and bleached by annealing after irradiation (figure 7a
insert) [13 14]
Figure 7 OA spectra of non-coloured (a) and PL spectra of γ-coloured nano (bold curve) and bulk
(solid curve) crystalline structures (b) and the structures with various LiF contents (c)
34 PL spectra of the irradiated thin-film structures
Non-presented here PL spectra of γ-irradiated CaF2 nanocrystals are composed of the reference 425
nm band excited at the wavelength of 370 nm The PL spectra of initial LiF crystal LiF and LiFCaF2
nanostructures having the same size of LiF nanocrystals and irradiated in analogous conditions are
given in figures 7bc In comparison with the initial crystals an increase of F3+-CCs excitation in the
region of Mg colloids absorption in nanostructures is observed together with an enhanced emission in
the green region with respect to the red one for γ-irradiated film structures (figures 7b) The
normalized emission spectra of nanostructures with various LiF content (bold) have the same shape
the F3+ photoluminescence band intensity at λmax = 538 nm increases of the same factor in comparison
with the F2 emission at 670 nm with respect to the spectrum of the crystal (solid curve) The PL
spectra show an increase (correlated with LiF nanocrystal content) of the intensities of F3+ and F2
bands (figure 7c) These results could be explained by the high structural and optical qualities of these
nanostructures (the overall emission is proportional to the quantity of luminescent LiF nanocrystals)
and by the nanocrystal purity with metal excess collection in their boundaries regions [22]
4 Thin-film structures with semiconductor and dielectric nanocrystals We measured nonlinear optical (NLO) effects for the reference films (figure 8a curve 1) elaborated
multilayers (figure 8a curves 2 3) and specially-elaborated multipeak TFIs containing c-oriented
cubic CdS nanocrystals of defined sizes as reported in figure 8 Sample 3 and TFIs intermediate layers
are composite film structures with semiconductor (CdS) and dielectric (CaF2) nanocrystals (figure 1c)
Separation of the transient shift and absorption saturation in TFIs gives us the features of both effects
Characteristic 1ndash2 ps decay of the shift confirms the metal clusters nature of the effect [23 24]
Maximal NLO effects in nanocrystals are increased with size reduction and are enhanced by extra
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
8
excitation power pulse durability [20 22] and γ-irradiation [19] These effects can be explained by
accumulation of colloids and electrons at nanocrystal boundaries
Figure 8 NLO characteristics detected for (a) reference films (1) multilayers (2 3) (b) multipeak
TFIs with c-oriented cubic CdS nanocrystals of defined sizes (c) Transmission spectra of the TFI
before (B) and at time of excitation (time delay between the excitation and registration is zero) (A)
Impurities and nonstoichiometric excess tend to be expelled from the small crystalline core as the
distance a defect or impurity must move to reach the surface of a nanocrystal is very small
Self-purification of the nanocrystals can be explained through technological arguments and is an
intrinsic property of defects in nanocrystals prepared by the methods of alternative deposition of
nanolayers with thicknesses 150ndash10 nm Post-growth thermal treatments ionising radiation
bombardment and light irradiation of the nanocrystals are the next tools for the nanocrystal
purification metal colloids formation and the nanocrystal properties modification
5 Conclusion
The c-axis highly oriented thin-film multilayer structures composed of dielectric (LiF CaF2) and
semiconductor (CdS) nanocrystals prepared by thermal evaporation show enhanced photo-response
which is related to high-quality nanocrystals but at the same time depends strongly on the defect
content especially as far as their 1ndash2 ps nonlinearities are concerned Critical factors are nanocrystal
purity as well as metal impurities and nonstoichiometric excess collection in their boundaries regions
The nanostructures (more high-quality than original bulk structures) can be part of efficient emitting
elements detectors and modulators of light as well as a novel type of dosimeters Such optically
stimulated luminescence dosimeters (integrable with SiO2OH fibres) provide capability for remote
monitoring radiation locations which are difficult to access and hazardous These devices are relatively
simple small in size cheap in production and have low power consumption Moreover they are also
suitable for space radiation dose exploration In addition they can be used in other radiation
measurements and have interesting perspectives in the case of periodical nanostructures composed of
the nanolayers of CdS and LiF nanocrystals with high-contrast indices of refraction (figure 1c)
Acknowledgments
The authors are indebted to O Bilan A Pace and V Gremenok for their help in irradiation and
microstructure testing of the samples Many thanks are due to M A Vincenti S Tikhomirov and O
Buganov for their assistance during PL and NLO experiments This work is supported by the
Belarusian National Program for Crystalline and Molecular Structures Research Project CMS-35 and
by the grants of the ENEA Fellowships Programme (Frascati Research Center Rome Italy)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
9
6 References
[1] Poole Ch and Owens F 2003 Introduction to Nanotechnology (New York John Wiley)
[2] Goncharova O 1994 Semiconductor microcrystallites in thin-film matrix fabrication methods
optical properties and application prospects New Materials for Thin Film Functional
Electronic-Technological Components ed V Labunov (Minsk Nauka i Tekhnika) chapter 6
pp 99ndash176
[3] Baldacchini G Cremona M dAuria G Martelli S Montereali R M Montecchi M Burattini E
Grilli A and Raco A 1996 Nucl Instr Meth B 116 447ndash51
[4] Montereali R M 2002 Point Defects in Thin Insulating films of Lithium Fluoride for Optical
Microsystems Ferroelectric and Dielectric Thin Films (Handbook of Thin Films Materials
vol 3) ed H S Nalwa (New York Academic Press) chapter 7 pp 399ndash431
[5] Kumar M et al 2005 J Phys D Appl Phys 38 637ndash41
[6] Goncharova O 2005 Microstructure and properties of periodic multilayer thin-film structures
with nanocrystals Advances in Spectroscopy for Lasers and Sensing Proc NATO Advanced
Study Institute (Erice Sicily Italy 6ndash21 June 2005) (NATO Science Series II
Mathematics Physics and Chemistry vol 231) ed B Di Bartolo and O Forte (Berlin
Springer) p 556
[7] Goncharova O Karpushko F V and Sinitsyn G V 1983 Technical Physics 28 1142ndash44
[8] Pulker H K 1979 Appl Optics 18 1969ndash77
[9] Wang Y H Lu J D Wang R W Mao Y L and Cheng Y G 2008 Vacuum 82 1220ndash23
[10] Bryukvina L I Ermolaeva E A Pidgurskii S N Suvorova L F and Khulugurov V M 2006 Phys
Sol State 48 68ndash72
[11] Schwartz K K Lyushina A F and Vitol A Ya 1969 Sov Phys Sol State 11 1885ndash90
[12] Lushchik A Lushchik Ch Schwartz K Vasilchenko E Papaleo R Sorokin M Volkov A E
Neumann R and Trautmann C 2007 Phys Rev B 76 054114
[13] Baldacchini G Goncharova O Kalinov V S Montereali R M Nichelatti E Vincenti A and
Voitovich A P 2007 Phys Status Solidi C 4 744ndash48
[14] Baldacchini G Goncharova O Kalinov V S Montereali R M Vincenti A and Voitovich A P
2007 Phys Status Solidi C 4 1134ndash38
[15] Goncharova O and Demin V 1993 Photosensitive resistive nonlinear optical thin-film
heterostructures RF Patent 2089656
[16] Goncharova O and Demin V 1994 Photosensitive resistive nonlinear optical composite films
RF Patent 2103846
[17] Goncharova O and Demin V 1994 Narrow-band thin-film FabryndashPerot interferometer RF
Patent 2078358
[18] Goncharova O 1998 Light-induced ultrafast bleaching in films of different arranging of
semiconductor nanocrystals materials Proc Int Conf on Coherent and Nonlinear Optics
(Moscow Russia 29 June ndash 3 July 1998) (Moscow Moscow State University Press) p 246
[19] Goncharova O Kalinov V and Voitovich A 2004 Radiat Meas 38 775ndash79
[20] Goncharova O 1996 Picosecond all-optical switching in thin-film FabryndashPerot interferometers
and cavityless devices Notes and Perspectives of Nonlinear Optics (Nonlinear Optics vol 3)
ed O Keller (London World Scientific) pp 636ndash42
[21] Goncharova O and Gremenok V 2007 Comparative study of electronic structure of thin film
nanocrystals prepared by low-temperature vacuum deposition Proc Int Conf CLEOEurope-
2007 (Munich Germany 17ndash22 June 2007) p 1-1
[22] Goncharova O Montereali R M and Baldacchini G 2008 Abstr Int Conf ICL-2008 Lyon
France 7ndash11 July 2008) p 160
[23] Goncharova O 1996 Studies on a Nature of the Picosecond Transient Absorption in Thin Films
Activated by Semiconductor or Metal Nanocrystals Proc Int Conf EQEC-1996 (Hamburg
Germany 8ndash13 Sept 1996) p 87
[24] Z Lu and K Zhu 2008 J Phys B At Mol Opt Phys 41 185503ndash09
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
10
33 Optical absorption features of non-irradiated thin-film structures
OA spectra of non-irradiated LiF nanostructures and initial crystals with small content of Mg2+
O2ndash
and OHndash ions [13] show well-resolved absorption of Mg
2+ colloids [11 12] (figure 7a) (The non-
irradiated and γ-irradiated substrates remain non-absorbing in the above spectral range) According to
the literature besides Mg colloids with the absorption band peaked at 44ndash46 eV the low-wavelength
absorption band at 36ndash41 eV related to the formation of more large Mg colloids or intrinsic Li
colloids [11 12] are reliably distinguished in non-irradiated LiF nanostructures (figure 7a) [21] and
initial crystals γ-irradiated with various doses and bleached by annealing after irradiation (figure 7a
insert) [13 14]
Figure 7 OA spectra of non-coloured (a) and PL spectra of γ-coloured nano (bold curve) and bulk
(solid curve) crystalline structures (b) and the structures with various LiF contents (c)
34 PL spectra of the irradiated thin-film structures
Non-presented here PL spectra of γ-irradiated CaF2 nanocrystals are composed of the reference 425
nm band excited at the wavelength of 370 nm The PL spectra of initial LiF crystal LiF and LiFCaF2
nanostructures having the same size of LiF nanocrystals and irradiated in analogous conditions are
given in figures 7bc In comparison with the initial crystals an increase of F3+-CCs excitation in the
region of Mg colloids absorption in nanostructures is observed together with an enhanced emission in
the green region with respect to the red one for γ-irradiated film structures (figures 7b) The
normalized emission spectra of nanostructures with various LiF content (bold) have the same shape
the F3+ photoluminescence band intensity at λmax = 538 nm increases of the same factor in comparison
with the F2 emission at 670 nm with respect to the spectrum of the crystal (solid curve) The PL
spectra show an increase (correlated with LiF nanocrystal content) of the intensities of F3+ and F2
bands (figure 7c) These results could be explained by the high structural and optical qualities of these
nanostructures (the overall emission is proportional to the quantity of luminescent LiF nanocrystals)
and by the nanocrystal purity with metal excess collection in their boundaries regions [22]
4 Thin-film structures with semiconductor and dielectric nanocrystals We measured nonlinear optical (NLO) effects for the reference films (figure 8a curve 1) elaborated
multilayers (figure 8a curves 2 3) and specially-elaborated multipeak TFIs containing c-oriented
cubic CdS nanocrystals of defined sizes as reported in figure 8 Sample 3 and TFIs intermediate layers
are composite film structures with semiconductor (CdS) and dielectric (CaF2) nanocrystals (figure 1c)
Separation of the transient shift and absorption saturation in TFIs gives us the features of both effects
Characteristic 1ndash2 ps decay of the shift confirms the metal clusters nature of the effect [23 24]
Maximal NLO effects in nanocrystals are increased with size reduction and are enhanced by extra
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
8
excitation power pulse durability [20 22] and γ-irradiation [19] These effects can be explained by
accumulation of colloids and electrons at nanocrystal boundaries
Figure 8 NLO characteristics detected for (a) reference films (1) multilayers (2 3) (b) multipeak
TFIs with c-oriented cubic CdS nanocrystals of defined sizes (c) Transmission spectra of the TFI
before (B) and at time of excitation (time delay between the excitation and registration is zero) (A)
Impurities and nonstoichiometric excess tend to be expelled from the small crystalline core as the
distance a defect or impurity must move to reach the surface of a nanocrystal is very small
Self-purification of the nanocrystals can be explained through technological arguments and is an
intrinsic property of defects in nanocrystals prepared by the methods of alternative deposition of
nanolayers with thicknesses 150ndash10 nm Post-growth thermal treatments ionising radiation
bombardment and light irradiation of the nanocrystals are the next tools for the nanocrystal
purification metal colloids formation and the nanocrystal properties modification
5 Conclusion
The c-axis highly oriented thin-film multilayer structures composed of dielectric (LiF CaF2) and
semiconductor (CdS) nanocrystals prepared by thermal evaporation show enhanced photo-response
which is related to high-quality nanocrystals but at the same time depends strongly on the defect
content especially as far as their 1ndash2 ps nonlinearities are concerned Critical factors are nanocrystal
purity as well as metal impurities and nonstoichiometric excess collection in their boundaries regions
The nanostructures (more high-quality than original bulk structures) can be part of efficient emitting
elements detectors and modulators of light as well as a novel type of dosimeters Such optically
stimulated luminescence dosimeters (integrable with SiO2OH fibres) provide capability for remote
monitoring radiation locations which are difficult to access and hazardous These devices are relatively
simple small in size cheap in production and have low power consumption Moreover they are also
suitable for space radiation dose exploration In addition they can be used in other radiation
measurements and have interesting perspectives in the case of periodical nanostructures composed of
the nanolayers of CdS and LiF nanocrystals with high-contrast indices of refraction (figure 1c)
Acknowledgments
The authors are indebted to O Bilan A Pace and V Gremenok for their help in irradiation and
microstructure testing of the samples Many thanks are due to M A Vincenti S Tikhomirov and O
Buganov for their assistance during PL and NLO experiments This work is supported by the
Belarusian National Program for Crystalline and Molecular Structures Research Project CMS-35 and
by the grants of the ENEA Fellowships Programme (Frascati Research Center Rome Italy)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
9
6 References
[1] Poole Ch and Owens F 2003 Introduction to Nanotechnology (New York John Wiley)
[2] Goncharova O 1994 Semiconductor microcrystallites in thin-film matrix fabrication methods
optical properties and application prospects New Materials for Thin Film Functional
Electronic-Technological Components ed V Labunov (Minsk Nauka i Tekhnika) chapter 6
pp 99ndash176
[3] Baldacchini G Cremona M dAuria G Martelli S Montereali R M Montecchi M Burattini E
Grilli A and Raco A 1996 Nucl Instr Meth B 116 447ndash51
[4] Montereali R M 2002 Point Defects in Thin Insulating films of Lithium Fluoride for Optical
Microsystems Ferroelectric and Dielectric Thin Films (Handbook of Thin Films Materials
vol 3) ed H S Nalwa (New York Academic Press) chapter 7 pp 399ndash431
[5] Kumar M et al 2005 J Phys D Appl Phys 38 637ndash41
[6] Goncharova O 2005 Microstructure and properties of periodic multilayer thin-film structures
with nanocrystals Advances in Spectroscopy for Lasers and Sensing Proc NATO Advanced
Study Institute (Erice Sicily Italy 6ndash21 June 2005) (NATO Science Series II
Mathematics Physics and Chemistry vol 231) ed B Di Bartolo and O Forte (Berlin
Springer) p 556
[7] Goncharova O Karpushko F V and Sinitsyn G V 1983 Technical Physics 28 1142ndash44
[8] Pulker H K 1979 Appl Optics 18 1969ndash77
[9] Wang Y H Lu J D Wang R W Mao Y L and Cheng Y G 2008 Vacuum 82 1220ndash23
[10] Bryukvina L I Ermolaeva E A Pidgurskii S N Suvorova L F and Khulugurov V M 2006 Phys
Sol State 48 68ndash72
[11] Schwartz K K Lyushina A F and Vitol A Ya 1969 Sov Phys Sol State 11 1885ndash90
[12] Lushchik A Lushchik Ch Schwartz K Vasilchenko E Papaleo R Sorokin M Volkov A E
Neumann R and Trautmann C 2007 Phys Rev B 76 054114
[13] Baldacchini G Goncharova O Kalinov V S Montereali R M Nichelatti E Vincenti A and
Voitovich A P 2007 Phys Status Solidi C 4 744ndash48
[14] Baldacchini G Goncharova O Kalinov V S Montereali R M Vincenti A and Voitovich A P
2007 Phys Status Solidi C 4 1134ndash38
[15] Goncharova O and Demin V 1993 Photosensitive resistive nonlinear optical thin-film
heterostructures RF Patent 2089656
[16] Goncharova O and Demin V 1994 Photosensitive resistive nonlinear optical composite films
RF Patent 2103846
[17] Goncharova O and Demin V 1994 Narrow-band thin-film FabryndashPerot interferometer RF
Patent 2078358
[18] Goncharova O 1998 Light-induced ultrafast bleaching in films of different arranging of
semiconductor nanocrystals materials Proc Int Conf on Coherent and Nonlinear Optics
(Moscow Russia 29 June ndash 3 July 1998) (Moscow Moscow State University Press) p 246
[19] Goncharova O Kalinov V and Voitovich A 2004 Radiat Meas 38 775ndash79
[20] Goncharova O 1996 Picosecond all-optical switching in thin-film FabryndashPerot interferometers
and cavityless devices Notes and Perspectives of Nonlinear Optics (Nonlinear Optics vol 3)
ed O Keller (London World Scientific) pp 636ndash42
[21] Goncharova O and Gremenok V 2007 Comparative study of electronic structure of thin film
nanocrystals prepared by low-temperature vacuum deposition Proc Int Conf CLEOEurope-
2007 (Munich Germany 17ndash22 June 2007) p 1-1
[22] Goncharova O Montereali R M and Baldacchini G 2008 Abstr Int Conf ICL-2008 Lyon
France 7ndash11 July 2008) p 160
[23] Goncharova O 1996 Studies on a Nature of the Picosecond Transient Absorption in Thin Films
Activated by Semiconductor or Metal Nanocrystals Proc Int Conf EQEC-1996 (Hamburg
Germany 8ndash13 Sept 1996) p 87
[24] Z Lu and K Zhu 2008 J Phys B At Mol Opt Phys 41 185503ndash09
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
10
excitation power pulse durability [20 22] and γ-irradiation [19] These effects can be explained by
accumulation of colloids and electrons at nanocrystal boundaries
Figure 8 NLO characteristics detected for (a) reference films (1) multilayers (2 3) (b) multipeak
TFIs with c-oriented cubic CdS nanocrystals of defined sizes (c) Transmission spectra of the TFI
before (B) and at time of excitation (time delay between the excitation and registration is zero) (A)
Impurities and nonstoichiometric excess tend to be expelled from the small crystalline core as the
distance a defect or impurity must move to reach the surface of a nanocrystal is very small
Self-purification of the nanocrystals can be explained through technological arguments and is an
intrinsic property of defects in nanocrystals prepared by the methods of alternative deposition of
nanolayers with thicknesses 150ndash10 nm Post-growth thermal treatments ionising radiation
bombardment and light irradiation of the nanocrystals are the next tools for the nanocrystal
purification metal colloids formation and the nanocrystal properties modification
5 Conclusion
The c-axis highly oriented thin-film multilayer structures composed of dielectric (LiF CaF2) and
semiconductor (CdS) nanocrystals prepared by thermal evaporation show enhanced photo-response
which is related to high-quality nanocrystals but at the same time depends strongly on the defect
content especially as far as their 1ndash2 ps nonlinearities are concerned Critical factors are nanocrystal
purity as well as metal impurities and nonstoichiometric excess collection in their boundaries regions
The nanostructures (more high-quality than original bulk structures) can be part of efficient emitting
elements detectors and modulators of light as well as a novel type of dosimeters Such optically
stimulated luminescence dosimeters (integrable with SiO2OH fibres) provide capability for remote
monitoring radiation locations which are difficult to access and hazardous These devices are relatively
simple small in size cheap in production and have low power consumption Moreover they are also
suitable for space radiation dose exploration In addition they can be used in other radiation
measurements and have interesting perspectives in the case of periodical nanostructures composed of
the nanolayers of CdS and LiF nanocrystals with high-contrast indices of refraction (figure 1c)
Acknowledgments
The authors are indebted to O Bilan A Pace and V Gremenok for their help in irradiation and
microstructure testing of the samples Many thanks are due to M A Vincenti S Tikhomirov and O
Buganov for their assistance during PL and NLO experiments This work is supported by the
Belarusian National Program for Crystalline and Molecular Structures Research Project CMS-35 and
by the grants of the ENEA Fellowships Programme (Frascati Research Center Rome Italy)
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
9
6 References
[1] Poole Ch and Owens F 2003 Introduction to Nanotechnology (New York John Wiley)
[2] Goncharova O 1994 Semiconductor microcrystallites in thin-film matrix fabrication methods
optical properties and application prospects New Materials for Thin Film Functional
Electronic-Technological Components ed V Labunov (Minsk Nauka i Tekhnika) chapter 6
pp 99ndash176
[3] Baldacchini G Cremona M dAuria G Martelli S Montereali R M Montecchi M Burattini E
Grilli A and Raco A 1996 Nucl Instr Meth B 116 447ndash51
[4] Montereali R M 2002 Point Defects in Thin Insulating films of Lithium Fluoride for Optical
Microsystems Ferroelectric and Dielectric Thin Films (Handbook of Thin Films Materials
vol 3) ed H S Nalwa (New York Academic Press) chapter 7 pp 399ndash431
[5] Kumar M et al 2005 J Phys D Appl Phys 38 637ndash41
[6] Goncharova O 2005 Microstructure and properties of periodic multilayer thin-film structures
with nanocrystals Advances in Spectroscopy for Lasers and Sensing Proc NATO Advanced
Study Institute (Erice Sicily Italy 6ndash21 June 2005) (NATO Science Series II
Mathematics Physics and Chemistry vol 231) ed B Di Bartolo and O Forte (Berlin
Springer) p 556
[7] Goncharova O Karpushko F V and Sinitsyn G V 1983 Technical Physics 28 1142ndash44
[8] Pulker H K 1979 Appl Optics 18 1969ndash77
[9] Wang Y H Lu J D Wang R W Mao Y L and Cheng Y G 2008 Vacuum 82 1220ndash23
[10] Bryukvina L I Ermolaeva E A Pidgurskii S N Suvorova L F and Khulugurov V M 2006 Phys
Sol State 48 68ndash72
[11] Schwartz K K Lyushina A F and Vitol A Ya 1969 Sov Phys Sol State 11 1885ndash90
[12] Lushchik A Lushchik Ch Schwartz K Vasilchenko E Papaleo R Sorokin M Volkov A E
Neumann R and Trautmann C 2007 Phys Rev B 76 054114
[13] Baldacchini G Goncharova O Kalinov V S Montereali R M Nichelatti E Vincenti A and
Voitovich A P 2007 Phys Status Solidi C 4 744ndash48
[14] Baldacchini G Goncharova O Kalinov V S Montereali R M Vincenti A and Voitovich A P
2007 Phys Status Solidi C 4 1134ndash38
[15] Goncharova O and Demin V 1993 Photosensitive resistive nonlinear optical thin-film
heterostructures RF Patent 2089656
[16] Goncharova O and Demin V 1994 Photosensitive resistive nonlinear optical composite films
RF Patent 2103846
[17] Goncharova O and Demin V 1994 Narrow-band thin-film FabryndashPerot interferometer RF
Patent 2078358
[18] Goncharova O 1998 Light-induced ultrafast bleaching in films of different arranging of
semiconductor nanocrystals materials Proc Int Conf on Coherent and Nonlinear Optics
(Moscow Russia 29 June ndash 3 July 1998) (Moscow Moscow State University Press) p 246
[19] Goncharova O Kalinov V and Voitovich A 2004 Radiat Meas 38 775ndash79
[20] Goncharova O 1996 Picosecond all-optical switching in thin-film FabryndashPerot interferometers
and cavityless devices Notes and Perspectives of Nonlinear Optics (Nonlinear Optics vol 3)
ed O Keller (London World Scientific) pp 636ndash42
[21] Goncharova O and Gremenok V 2007 Comparative study of electronic structure of thin film
nanocrystals prepared by low-temperature vacuum deposition Proc Int Conf CLEOEurope-
2007 (Munich Germany 17ndash22 June 2007) p 1-1
[22] Goncharova O Montereali R M and Baldacchini G 2008 Abstr Int Conf ICL-2008 Lyon
France 7ndash11 July 2008) p 160
[23] Goncharova O 1996 Studies on a Nature of the Picosecond Transient Absorption in Thin Films
Activated by Semiconductor or Metal Nanocrystals Proc Int Conf EQEC-1996 (Hamburg
Germany 8ndash13 Sept 1996) p 87
[24] Z Lu and K Zhu 2008 J Phys B At Mol Opt Phys 41 185503ndash09
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
10
6 References
[1] Poole Ch and Owens F 2003 Introduction to Nanotechnology (New York John Wiley)
[2] Goncharova O 1994 Semiconductor microcrystallites in thin-film matrix fabrication methods
optical properties and application prospects New Materials for Thin Film Functional
Electronic-Technological Components ed V Labunov (Minsk Nauka i Tekhnika) chapter 6
pp 99ndash176
[3] Baldacchini G Cremona M dAuria G Martelli S Montereali R M Montecchi M Burattini E
Grilli A and Raco A 1996 Nucl Instr Meth B 116 447ndash51
[4] Montereali R M 2002 Point Defects in Thin Insulating films of Lithium Fluoride for Optical
Microsystems Ferroelectric and Dielectric Thin Films (Handbook of Thin Films Materials
vol 3) ed H S Nalwa (New York Academic Press) chapter 7 pp 399ndash431
[5] Kumar M et al 2005 J Phys D Appl Phys 38 637ndash41
[6] Goncharova O 2005 Microstructure and properties of periodic multilayer thin-film structures
with nanocrystals Advances in Spectroscopy for Lasers and Sensing Proc NATO Advanced
Study Institute (Erice Sicily Italy 6ndash21 June 2005) (NATO Science Series II
Mathematics Physics and Chemistry vol 231) ed B Di Bartolo and O Forte (Berlin
Springer) p 556
[7] Goncharova O Karpushko F V and Sinitsyn G V 1983 Technical Physics 28 1142ndash44
[8] Pulker H K 1979 Appl Optics 18 1969ndash77
[9] Wang Y H Lu J D Wang R W Mao Y L and Cheng Y G 2008 Vacuum 82 1220ndash23
[10] Bryukvina L I Ermolaeva E A Pidgurskii S N Suvorova L F and Khulugurov V M 2006 Phys
Sol State 48 68ndash72
[11] Schwartz K K Lyushina A F and Vitol A Ya 1969 Sov Phys Sol State 11 1885ndash90
[12] Lushchik A Lushchik Ch Schwartz K Vasilchenko E Papaleo R Sorokin M Volkov A E
Neumann R and Trautmann C 2007 Phys Rev B 76 054114
[13] Baldacchini G Goncharova O Kalinov V S Montereali R M Nichelatti E Vincenti A and
Voitovich A P 2007 Phys Status Solidi C 4 744ndash48
[14] Baldacchini G Goncharova O Kalinov V S Montereali R M Vincenti A and Voitovich A P
2007 Phys Status Solidi C 4 1134ndash38
[15] Goncharova O and Demin V 1993 Photosensitive resistive nonlinear optical thin-film
heterostructures RF Patent 2089656
[16] Goncharova O and Demin V 1994 Photosensitive resistive nonlinear optical composite films
RF Patent 2103846
[17] Goncharova O and Demin V 1994 Narrow-band thin-film FabryndashPerot interferometer RF
Patent 2078358
[18] Goncharova O 1998 Light-induced ultrafast bleaching in films of different arranging of
semiconductor nanocrystals materials Proc Int Conf on Coherent and Nonlinear Optics
(Moscow Russia 29 June ndash 3 July 1998) (Moscow Moscow State University Press) p 246
[19] Goncharova O Kalinov V and Voitovich A 2004 Radiat Meas 38 775ndash79
[20] Goncharova O 1996 Picosecond all-optical switching in thin-film FabryndashPerot interferometers
and cavityless devices Notes and Perspectives of Nonlinear Optics (Nonlinear Optics vol 3)
ed O Keller (London World Scientific) pp 636ndash42
[21] Goncharova O and Gremenok V 2007 Comparative study of electronic structure of thin film
nanocrystals prepared by low-temperature vacuum deposition Proc Int Conf CLEOEurope-
2007 (Munich Germany 17ndash22 June 2007) p 1-1
[22] Goncharova O Montereali R M and Baldacchini G 2008 Abstr Int Conf ICL-2008 Lyon
France 7ndash11 July 2008) p 160
[23] Goncharova O 1996 Studies on a Nature of the Picosecond Transient Absorption in Thin Films
Activated by Semiconductor or Metal Nanocrystals Proc Int Conf EQEC-1996 (Hamburg
Germany 8ndash13 Sept 1996) p 87
[24] Z Lu and K Zhu 2008 J Phys B At Mol Opt Phys 41 185503ndash09
International Conference on Defects in Insulating Materials IOP PublishingJournal of Physics Conference Series 249 (2010) 012063 doi1010881742-65962491012063
10